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125問 • 2年前

問題一覧

Given a potential energy function U(x), the corresponding force F is in the positive x direction if:

U is a decreasing function of x

The thermal energy of a system consisting of a thrown ball, Earth, and the air is most closely associated with:

motions of individual particles within the ball and the air

Objects A and B interact with each other via both conservative and nonconservative forces. Let KA and KB be the kinetic energies, U be the potential energy, and Eint be the thermal energy. If no external agent does work on the objects then:

KA +KB +U +Eint is conserved

A block slides across a rough horizontal table top. The work done by friction changes:

only the kinetic and internal energies

Which one of the following statements is true?

none of the above

The center of mass of a uniform disk of radius R is located:

at the center

The center of mass of the system consisting of Earth, the Sun, and the planet Mars is:

closer to the Sun than to either of the other bodies

The center of mass of Earth’s atmosphere is:

near the center of Earth

A light rope passes over a light frictionless pulley attached to the ceiling. An object with a large mass is tied to one end and an object with a smaller mass is tied to the other end. Starting from rest the heavier object moves downward and the lighter object moves upward with the same magnitude acceleration. Which of the following statements is true for the system consisting of the two masses?

None of the above statements are true.

The center of mass of a system of particles has a constant velocity if:

the external forces acting on particles of the system sum to zero

The center of mass of a system of particles remains at the same place if:

it is initially at rest and the external forces sum to zero

A man sits in the back of a canoe in still water. He then moves to the front of the canoe and sits there. Afterwards the canoe:

is rearward of its original position and not moving

The center of mass of a system of particles obeys an equation similar to Newton’s second law F = ma com, where:

F is the net external force and m is the total mass of the system

Momentum may be expressed in:

N·s

The momentum of an object at a given instant is independent of its:

acceleration

Two objects, P and Q, have the same momentum. Q has more kinetic energy than P if it:

is moving faster than P

If the total momentum of a system is changing:

a net external force must be acting on the system

When you step on the accelerator to increase the speed of your car, the force that accelerates the car is:

the force of friction of the road on the tires

A projectile in flight explodes into several fragments. The total momentum of the fragments immediately after this explosion:

is the same as the momentum of the projectile immediately before the explosion

A rifle of mass M is initially at rest but free to recoil. It fires a bullet of mass m and velocity v (relative to the ground). After firing, the velocity of the rifle (relative to the ground) is:

−mv/M

Force:

equals the time rate of change of momentum

A cart loaded with sand slides forward along a horizontal frictionless track. As the cart moves, sand trickles out at a constant rate through a hole in the back of the cart. The acceleration of the cart is:

zero

The thrust of a rocket is:

the force of the exiting fuel gases on the rocket

The law of conservation of momentum applies to a system of colliding objects only if:

the net external impulse is zero

Two bodies of unequal mass, placed at rest on a frictionless surface, are acted on by equal horizontal forces for equal times. Just after these forces are removed, the body of greater mass will have:

the same momentum as the other body

ns: C 55. A student’s life was saved in an automobile accident because an airbag expanded in front of his head. If the car had not been equipped with an airbag, the windshield would have stopped the motion of his head in a much shorter time. Compared to the windshield, the airbag:

exerts a much smaller force

57. A golf ball of mass m is hit by a golf club so that the ball leaves the tee with speed v. The club is in contact with the ball for time T . The magnitude of the average force on the club on the ball during the time T is:

mv/T

Whenever an object strikes a stationary object of equal mass:

none of the above

For a two-body collision involving objects with different masses, a frame of reference which has the same velocity relative to the laboratory as does the center of mass of the two objects is:

a frame for which the total momentum of the two objects is zero

An inelastic collision is one in which:

momentum is conserved but kinetic energy is not conserved

For a completely inelastic two-body collision the kinetic energy retained by the objects is the same as

1/2Mv2 , where M is the total mass and v is the velocity of the center of mass

An elastic collision is one in which:

kinetic energy and momentum are both conserved

Object A strikes the stationary object B head-on in an elastic collision. The mass of A is fixed, you may choose the mass of B appropriately. Then:

for B to have the greatest recoil kinetic energy, choose mB = mA

When a particle suffers a head-on elastic collision with another particle, initially at rest, the greatest fraction of kinetic energy is transferred if:

the incident and target particle have the same mass

Two identical carts travel at 1 m/s in opposite directions on a common horizontal surface. They collide head-on and are reported to rebound, each with a speed of 2 m/s. Then:

if some other form of energy were changed to kinetic during the collision, the report could be true

If a wheel turns with constant angular speed then

the wheel turns through equal angles in equal times

If the angular velocity vector of a spinning body points out of the page then, when viewed from above the page, the body is spinning:

counterclockwise about an axis that is perpendicular to the page

The angular velocity vector of a spinning body points out of the page. If the angular acceleration vector points into the page then:

the body is slowing down

A car travels north at constant velocity. It goes over a piece of mud, which sticks to the tire. The initial acceleration of the mud, as it leaves the ground, is:

vertically upward

A wheel starts from rest and spins with a constant angular acceleration. As time goes on the acceleration vector for a point on the rim:

increases in magnitude and becomes more nearly radial

The rotational inertia of a wheel about its axle does not depend upon its:

speed of rotation

Two uniform circular disks having the same mass and the same thickness are made from different materials. The disk with the smaller rotational inertia is:

the one made from the more dense material

A uniform solid cylinder made of lead has the same mass and the same length as a uniform solid cylinder made of wood. The rotational inertia of the lead cylinder compared to the wooden one is:

less

When a thin uniform stick of mass M and length L is pivoted about its midpoint, its rotational inertia is ML2/12. When pivoted about a parallel axis through one end, its rotational inertia is:

ML2/3

The rotational inertia of a solid uniform sphere about a diameter is (2/5)MR2, where M is its mass and R is its radius. If the sphere is pivoted about an axis that is tangent to its surface, its rotational inertia is:

(7/5)MR2

A solid uniform sphere of radius R and mass M has a rotational inertia about a diameter that is given by (2/5)MR2. A light string of length 3R is attached to the surface and used to suspend the sphere from the ceiling. Its rotational inertia about the point of attachment at the ceiling is:

(82/5)MR2

A force with a given magnitude is to be applied to a wheel. The torque can be maximized by:

applying the force at the rim, tangent to the rim

τ = Iα for an object rotating about a fixed axis, where τ is the net torque acting on it, I is its rotational inertia, and α is its angular acceleration. This expression:

follows directly from Newton’s second law

A disk is free to rotate on a fixed axis. A force of given magnitude F , in the plane of the disk, is to be applied. Of the following alternatives the greatest angular acceleration is obtained if the force is:

applied tangentially at the rim

A block is attached to each end of a rope that passes over a pulley suspended from the ceiling. The blocks do not have the same mass. If the rope does not slip on the pulley, then at any instant after the blocks start moving, the rope:

pulls on both blocks, but exerts a greater force on the heavier block

A pulley with a radius of 3.0 cm and a rotational inertia of 4.5 × 10−3 kg · m2 is suspended from the ceiling. A rope passes over it with a 2.0-kg block attached to one end and a 4.0-kg block attached to the other. The rope does not slip on the pulley. At any instant after the blocks start moving, the object with the greatest kinetic energy is:

the pulley

A disk starts from rest and rotates around a fixed axis, subject to a constant net torque. The work done by the torque during the second 5 s is as the work done during the first 5 s.

four times as much

A disk starts from rest and rotates about a fixed axis, subject to a constant net torque. The work done by the torque during the second revolution is first revolution.

the same

Two wheels roll side-by-side without sliding, at the same speed. The radius of wheel 2 is twice the radius of wheel 1. The angular velocity of wheel 2 is:

more than twice the angular velocity of wheel 1

A forward force on the axle accelerates a rolling wheel on a horizontal surface. If the wheel does not slide the frictional force of the surface on the wheel is:

in the upward direction

When the speed of a rear-drive car is increasing on a horizontal road the direction of the frictional force on the tires is:

backward for the front tires and forward for the rear tires

A sphere and a cylinder of equal mass and radius are simultaneously released from rest on the same inclined plane and roll without sliding down the incline. Then:

none of the above are true

A hoop, a uniform disk, and a uniform sphere, all with the same mass and outer radius, start with the same speed and roll without sliding up identical inclines. Rank the objects according to how high they go, least to greatest.

hoop, disk, sphere

A hoop rolls with constant velocity and without sliding along level ground. Its rotational kinetic energy is:

the same as its translational kinetic energy

When we apply the energy conservation principle to a cylinder rolling down an incline without sliding, we exclude the work done by friction because:

the linear velocity of the point of contact (relative to the inclined surface) is zero

Two uniform cylinders have different masses and different rotational inertias. They simultaneously start from rest at the top of an inclined plane and roll without sliding down the plane. The cylinder that gets to the bottom first is:

neither (they arrive together)

The fundamental dimensions of angular momentum are:

none of these

Possible units of angular momentum are:

kg·m2 /s

The unit kg·m2/s can be used for:

angular momentum

The newton·second is a unit of:

linear momentum

The angular momentum vector of Earth about its rotation axis, due to its daily rotation, is directed:

north

A man, with his arms at his sides, is spinning on a light frictionless turntable. When he extends his arms:

his angular momentum remains the same

A man, holding a weight in each hand, stands at the center of a horizontal frictionless rotating turntable. The effect of the weights is to double the rotational inertia of the system. As he is rotating, the man opens his hands and drops the two weights. They fall outside the turntable. Then:

his angular velocity remains about the same

A uniform sphere of radius R rotates about a diameter with an angular momentum of magnitude L. Under the action of internal forces the sphere collapses to a uniform sphere of radius R/2. The magnitude of its new angular momentum is:

When a man on a frictionless rotating stool extends his arms horizontally, his rotational kinetic energy:

must decrease

When a woman on a frictionless rotating turntable extends her arms out horizontally, her angular momentum:

must remain the same

A phonograph record is dropped onto a freely spinning turntable. Then:

the total angular momentum remains constant

Two pendulum bobs of unequal mass are suspended from the same fixed point by strings of equal length. The lighter bob is drawn aside and then released so that it collides with the other bob on reaching the vertical position. The collision is elastic. What quantities are conserved in the collision?

Both kinetic energy and angular momentum of the system

A particle, held by a string whose other end is attached to a fixed point C, moves in a circle on a horizontal frictionless surface. If the string is cut, the angular momentum of the particle about the point C:

does not change

A net torque applied to a rigid object always tends to produce:

angular acceleration

The conditions that the net force and the net torque both vanish:

hold for every rigid body in equilibrium

For an object in equilibrium the net torque acting on it vanishes only if each torque is calculated about:

the same point

For a body to be in equilibrium under the combined action of several forces:

the sum of the components of all the forces in any direction must equal zero

For a body to be in equilibrium under the combined action of several forces:

the sum of the torques about any point must equal zero

To determine if a rigid body is in equilibrium the vector sum of the gravitational forces acting on the particles of the body can be replaced by a single force acting at:

the center of gravity

The center of gravity coincides with the center of mass:

if the acceleration due to gravity is uniform over the body

The location of which of the following points within an object might depend on the orientation of the object?

Its center of gravity

A cylinder placed so it can roll on a horizontal table top, with its center of gravity above its geometrical center, is:

in unstable equilibrium

A cylinder placed so it can roll on a horizontal table top, with its center of gravity below its geometrical center, is:

in stable equilibrium

A cube balanced with one edge in contact with a table top and with its center of gravity directly above the edge is in _____ equilibrium with respect to rotation about the edge and in ____ equilibrium with respect to rotation about a horizontal axis that is perpendicular to the edge.

unstable, stable

Stress can be measured in:

N/m2

Strain can be measured in:

none of these (it is unitless)

Young’s modulus can be correctly given in:

N/m2

Young’s modulus is a proportionality constant that relates the force per unit area applied perpendicularly at the surface of an object to:

the fractional change in length

Young’s modulus can be used to calculate the strain for a stress that is:

well below the yield strength

The ultimate strength of a sample is the stress at which the sample:

breaks

The bulk modulus is a proportionality constant that relates the pressure acting on an object to:

the fractional change in volume

To shear a cube-shaped object, forces of equal magnitude and opposite directions might be applied:

to opposite faces, parallel to the faces

In the formula F = Gm1m2/r2, the quantity G:

is a universal constant of nature

The magnitude of the acceleration of a planet in orbit around the Sun is proportional to:

the mass of the Sun

Suitable units for the gravitational constant G are:

m3 /(kg·s2 )

Earth exerts a gravitational force on the Moon, keeping it in its orbit. The reaction to this force, in the sense of Newton’s third law, is:

the gravitational force on Earth by the Moon

Let F1 be the magnitude of the gravitational force exerted on the Sun by Earth and F2 be the magnitude of the force exerted on Earth by the Sun. Then:

F1 is equal to F2

A rocket ship is coasting toward a planet. Its captain wishes to know the value of g at the surface of the planet. This may be inferred by:

observing the ship’s acceleration and correcting for the distance from the center of the planet

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The mass of an object:

is independent of the acceleration due to gravity

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問題一覧

Given a potential energy function U(x), the corresponding force F is in the positive x direction if:

U is a decreasing function of x

The thermal energy of a system consisting of a thrown ball, Earth, and the air is most closely associated with:

motions of individual particles within the ball and the air

KA +KB +U +Eint is conserved

A block slides across a rough horizontal table top. The work done by friction changes:

only the kinetic and internal energies

Which one of the following statements is true?

none of the above

The center of mass of a uniform disk of radius R is located:

at the center

The center of mass of the system consisting of Earth, the Sun, and the planet Mars is:

closer to the Sun than to either of the other bodies

The center of mass of Earth’s atmosphere is:

near the center of Earth

None of the above statements are true.

The center of mass of a system of particles has a constant velocity if:

the external forces acting on particles of the system sum to zero

The center of mass of a system of particles remains at the same place if:

it is initially at rest and the external forces sum to zero

A man sits in the back of a canoe in still water. He then moves to the front of the canoe and sits there. Afterwards the canoe:

is rearward of its original position and not moving

The center of mass of a system of particles obeys an equation similar to Newton’s second law F = ma com, where:

F is the net external force and m is the total mass of the system

Momentum may be expressed in:

N·s

The momentum of an object at a given instant is independent of its:

acceleration

Two objects, P and Q, have the same momentum. Q has more kinetic energy than P if it:

is moving faster than P

If the total momentum of a system is changing:

a net external force must be acting on the system

When you step on the accelerator to increase the speed of your car, the force that accelerates the car is:

the force of friction of the road on the tires

A projectile in flight explodes into several fragments. The total momentum of the fragments immediately after this explosion:

is the same as the momentum of the projectile immediately before the explosion

A rifle of mass M is initially at rest but free to recoil. It fires a bullet of mass m and velocity v (relative to the ground). After firing, the velocity of the rifle (relative to the ground) is:

−mv/M

Force:

equals the time rate of change of momentum

zero

The thrust of a rocket is:

the force of the exiting fuel gases on the rocket

The law of conservation of momentum applies to a system of colliding objects only if:

the net external impulse is zero

Two bodies of unequal mass, placed at rest on a frictionless surface, are acted on by equal horizontal forces for equal times. Just after these forces are removed, the body of greater mass will have:

the same momentum as the other body

exerts a much smaller force

mv/T

Whenever an object strikes a stationary object of equal mass:

none of the above

For a two-body collision involving objects with different masses, a frame of reference which has the same velocity relative to the laboratory as does the center of mass of the two objects is:

a frame for which the total momentum of the two objects is zero

An inelastic collision is one in which:

momentum is conserved but kinetic energy is not conserved

For a completely inelastic two-body collision the kinetic energy retained by the objects is the same as

1/2Mv2 , where M is the total mass and v is the velocity of the center of mass

An elastic collision is one in which:

kinetic energy and momentum are both conserved

Object A strikes the stationary object B head-on in an elastic collision. The mass of A is fixed, you may choose the mass of B appropriately. Then:

for B to have the greatest recoil kinetic energy, choose mB = mA

When a particle suffers a head-on elastic collision with another particle, initially at rest, the greatest fraction of kinetic energy is transferred if:

the incident and target particle have the same mass

Two identical carts travel at 1 m/s in opposite directions on a common horizontal surface. They collide head-on and are reported to rebound, each with a speed of 2 m/s. Then:

if some other form of energy were changed to kinetic during the collision, the report could be true

If a wheel turns with constant angular speed then

the wheel turns through equal angles in equal times

If the angular velocity vector of a spinning body points out of the page then, when viewed from above the page, the body is spinning:

counterclockwise about an axis that is perpendicular to the page

The angular velocity vector of a spinning body points out of the page. If the angular acceleration vector points into the page then:

the body is slowing down

A car travels north at constant velocity. It goes over a piece of mud, which sticks to the tire. The initial acceleration of the mud, as it leaves the ground, is:

vertically upward

A wheel starts from rest and spins with a constant angular acceleration. As time goes on the acceleration vector for a point on the rim:

increases in magnitude and becomes more nearly radial

The rotational inertia of a wheel about its axle does not depend upon its:

speed of rotation

Two uniform circular disks having the same mass and the same thickness are made from different materials. The disk with the smaller rotational inertia is:

the one made from the more dense material

A uniform solid cylinder made of lead has the same mass and the same length as a uniform solid cylinder made of wood. The rotational inertia of the lead cylinder compared to the wooden one is:

less

When a thin uniform stick of mass M and length L is pivoted about its midpoint, its rotational inertia is ML2/12. When pivoted about a parallel axis through one end, its rotational inertia is:

ML2/3

(7/5)MR2

(82/5)MR2

A force with a given magnitude is to be applied to a wheel. The torque can be maximized by:

applying the force at the rim, tangent to the rim

τ = Iα for an object rotating about a fixed axis, where τ is the net torque acting on it, I is its rotational inertia, and α is its angular acceleration. This expression:

follows directly from Newton’s second law

applied tangentially at the rim

pulls on both blocks, but exerts a greater force on the heavier block

the pulley

A disk starts from rest and rotates around a fixed axis, subject to a constant net torque. The work done by the torque during the second 5 s is as the work done during the first 5 s.

four times as much

A disk starts from rest and rotates about a fixed axis, subject to a constant net torque. The work done by the torque during the second revolution is first revolution.

the same

Two wheels roll side-by-side without sliding, at the same speed. The radius of wheel 2 is twice the radius of wheel 1. The angular velocity of wheel 2 is:

more than twice the angular velocity of wheel 1

A forward force on the axle accelerates a rolling wheel on a horizontal surface. If the wheel does not slide the frictional force of the surface on the wheel is:

in the upward direction

When the speed of a rear-drive car is increasing on a horizontal road the direction of the frictional force on the tires is:

backward for the front tires and forward for the rear tires

A sphere and a cylinder of equal mass and radius are simultaneously released from rest on the same inclined plane and roll without sliding down the incline. Then:

none of the above are true

hoop, disk, sphere

A hoop rolls with constant velocity and without sliding along level ground. Its rotational kinetic energy is:

the same as its translational kinetic energy

When we apply the energy conservation principle to a cylinder rolling down an incline without sliding, we exclude the work done by friction because:

the linear velocity of the point of contact (relative to the inclined surface) is zero

neither (they arrive together)

The fundamental dimensions of angular momentum are:

none of these

Possible units of angular momentum are:

kg·m2 /s

The unit kg·m2/s can be used for:

angular momentum

The newton·second is a unit of:

linear momentum

The angular momentum vector of Earth about its rotation axis, due to its daily rotation, is directed:

north

A man, with his arms at his sides, is spinning on a light frictionless turntable. When he extends his arms:

his angular momentum remains the same

his angular velocity remains about the same

When a man on a frictionless rotating stool extends his arms horizontally, his rotational kinetic energy:

must decrease

When a woman on a frictionless rotating turntable extends her arms out horizontally, her angular momentum:

must remain the same

A phonograph record is dropped onto a freely spinning turntable. Then:

the total angular momentum remains constant

Both kinetic energy and angular momentum of the system

does not change

A net torque applied to a rigid object always tends to produce:

angular acceleration

The conditions that the net force and the net torque both vanish:

hold for every rigid body in equilibrium

For an object in equilibrium the net torque acting on it vanishes only if each torque is calculated about:

the same point

For a body to be in equilibrium under the combined action of several forces:

the sum of the components of all the forces in any direction must equal zero

For a body to be in equilibrium under the combined action of several forces:

the sum of the torques about any point must equal zero

To determine if a rigid body is in equilibrium the vector sum of the gravitational forces acting on the particles of the body can be replaced by a single force acting at:

the center of gravity

The center of gravity coincides with the center of mass:

if the acceleration due to gravity is uniform over the body

The location of which of the following points within an object might depend on the orientation of the object?

Its center of gravity

A cylinder placed so it can roll on a horizontal table top, with its center of gravity above its geometrical center, is:

in unstable equilibrium

A cylinder placed so it can roll on a horizontal table top, with its center of gravity below its geometrical center, is:

in stable equilibrium

unstable, stable

Stress can be measured in:

N/m2

Strain can be measured in:

none of these (it is unitless)

Young’s modulus can be correctly given in:

N/m2

Young’s modulus is a proportionality constant that relates the force per unit area applied perpendicularly at the surface of an object to:

the fractional change in length

Young’s modulus can be used to calculate the strain for a stress that is:

well below the yield strength

The ultimate strength of a sample is the stress at which the sample:

breaks

The bulk modulus is a proportionality constant that relates the pressure acting on an object to:

the fractional change in volume

To shear a cube-shaped object, forces of equal magnitude and opposite directions might be applied:

to opposite faces, parallel to the faces

In the formula F = Gm1m2/r2, the quantity G:

is a universal constant of nature

The magnitude of the acceleration of a planet in orbit around the Sun is proportional to:

the mass of the Sun

Suitable units for the gravitational constant G are:

m3 /(kg·s2 )

Earth exerts a gravitational force on the Moon, keeping it in its orbit. The reaction to this force, in the sense of Newton’s third law, is:

the gravitational force on Earth by the Moon

Let F1 be the magnitude of the gravitational force exerted on the Sun by Earth and F2 be the magnitude of the force exerted on Earth by the Sun. Then:

F1 is equal to F2

A rocket ship is coasting toward a planet. Its captain wishes to know the value of g at the surface of the planet. This may be inferred by:

observing the ship’s acceleration and correcting for the distance from the center of the planet

100

The mass of an object:

is independent of the acceleration due to gravity