Chapter 9

Question 1

The SI units of momentum are

Answer 1

kg*m/s

Question 2

If a body moves in such a way that its linear momentum is constant, then

Answer 2

the sum of all the forces acting on it must be zero

Question 3

Two identical bodies of mass M move with equal speeds v. The direction of their velocities is illustrated in the figure. The magnitude of the linear momentum of the system is

Answer 3

(Sq. Rt. 2)Mv

Question 4

A 40 kg girl standing at rest on the ice gives a 60 kg boy, who is also standing at rest on the ice a shove. After the shove, the boy is moving backward at 2 m/s. Ignore friction. The girl’s speed is

Answer 4

3 m/s

Question 5

Two students, sitting on frictionless carts, push against each other. Both are initially at rest. The mass of Susan and her cart is M, and mass of Bob and his cart is 1.5M. If Susan pushes Bob so that she recoils with velocity -v, what is the velocity of Bob?

Answer 5

+2v/3

Question 6

If the momentum of a mass M is doubled, its kinetic energy will be multiplied by a factor of

Answer 6

4

Question 7

If you take the derivative of the kinetic energy of a particle with respect to its velocity you get

Answer 7

Momentum

Question 8

Two mass M and 5M rest on a horizontal frictionless table with a compressed spring of negligible mass between them. When the spring is released, the energy of the spring is shared between the two masses in such a way that

Answer 8

M gets 5/6 of the energy

Question 9

A golf ball and a Ping-pong ball are dropped in a vacuum chamber. When they have fallen halfway to the floor, they have the same

Answer 9

Speed

Question 10

Impulse -

Answer 10

Average Force x Time = mass x delta velocity

Question 11

Suppose a ping-pong ball and a bowling ball are rolling toward you. Both have the same momentum, and you exert the same force to stop each. How do the time intervals to stop them compare?

Answer 11

Both take the same time

Question 12

Suppose a person jumps on the surface of Earth. The Earth

Answer 12

will recoil in the opposite direction with tiny velocity

Question 13

What is the physical significance of the area under the curve of Force vs. Time?

Answer 13

Impulse

Question 14

A 4.0 kg block, initially at rest, experiences a force that varies with time as shown in the figure. When t = 6.0 ms, the speed of the block is

Answer 14

3.0 m/s (if chart goes from 0-4 in 3.5s and 4-0 in 3.5-6 s)

Question 15

A ball of mass m strikes a wall that is perpendicular to its path at speed +v and rebounds in the opposite direction with a speed -v. The impulse imparted to the ball by the wall is

Answer 15

-2mv

Question 16

Two balls are dropped from a height of 6 m. Ball A bounces up to a height of 4 m whereas ball B bounces up to 2 m. Which ball experiences the larger impulse during its collision with the floor?

Answer 16

It is impossible to tell without knowing the masses of the balls.

Question 17

In all collisions of short duration and for which it is true that no external forces act on the collision participants

Answer 17

Momentum is conserved

Question 18

For a system consisting of two particles that undergo an elastic collision,

Answer 18

Both kinetic energy and momentum are conserved

Question 19

Two cars of equal mass travel in opposite directions at equal speeds. They collide in a perfectly INELASTIC collision. Just after the collision, their velocities are

Answer 19

zero

Question 20

Two equal masses travel in opposite directions with equal speed. If they collide in a perfectly ELASTIC collision, then just after the collision their velocities will be

Answer 20

Equal in magnitude but opposite in direction from their original velocities

Question 21

Two equal masses travel in opposite directions with equal speed. If they collide in a collision that is between elastic and inelastic. Just after the collision, their velocities are

Answer 21

Less in magnitude and opposite in direction from their original velocities

Question 22

The figure shows a ballistic pendulum in three states. Which of the following statements is true?

Answer 22

The total mechanical energy is conserved after the collision

Question 23

Two particles m1 and m2 each with mass m are moving with velocity -v and 2v, respectively. The momentum of m1 relative to the center-of-mass is

Answer 23

-3/2mv

Question 24

A man in a spacecraft that is moving with a velocity Vo in free space runs forward and then stops. The center o mass of the system (that is, the ship and the man)

Answer 24

Continues all the while at its original velocity