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Unit 1. Newtonian Mechanics
IV. Linear momentum

1.Consider the two blocks in the above diagram. The left-hand block has mass 2m; the right-hand block has mass m. Which of the marked locations represents the center of mass of the two-block system?
A
B
C
D
E
2.As a classroom demonstration, a student is asked to knock a large block down by throwing a ball at it. The student is given a choice of two types of balls. Both are equal radius and mass:

I.  a spongy ball, which thuds off of the block without much bounce.
II. a bouncy ball, which rebounds from the block with considerable speed.

Which ball should the student use, and why?
Ball II: since ball I comes to rest, it has zero momentum after the collision, and so cannot apply a force to the large block.
Ball I: since its initial kinetic energy is almost entirely converted to heat, this heat energy is more likely to knock down the block.
It doesn't matter: since the balls are the same mass and (presumably) moving at the same speed upon impact, both should generate the same impulse on the block.
Ball II: the ball's momentum change upon striking the block is nearly twice its initial momentum due to the rebound. Thus, it applies more impulse to the large block than ball I.
Ball I: since ball II rebounds, its momentum change is nearly zero. Thus, it can not apply much impulse to the block. Ball I, though, changes its momentum by coming to rest.
3.A 2.0 kg cart moves to the right at a speed of 3.0 m/s toward a resting 4 kg cart. The carts collide, after which the 2 kg cart is moving to the left at 1.0 m/s. What is the speed of the 4 kg cart after the collision?
0 m/s
0.5 m/s
1.0 m/s
1.5 m/s
2.0 m/s
Questions 4 & 5 refer to the image below

A 6.0 kg cart and a 3.0 kg cart are connected by a compressed spring, as shown above. The spring uncoils, pushing the carts apart. The 3 kg cart moves at 4.0 m/s after the uncoiling.

4.After the spring uncoils, what is the combined momentum of the two carts?
0 Ns
2 Ns
3 Ns
6 Ns
12 Ns
5.How much energy was released by the spring when it uncoiled?
0 J
12 J
24 J
36 J
48 J
6.A ball of mass m moving to the right at speed v collides elastically with a pivoted bar of mass M and moment of inertia I, as shown above. The angular speed of the bar immediately after collision is ω, the rebound speed of the ball is v'. Which of the following is a correct expression for conservation of energy in this collision?
7.A ball of putty collides with and sticks to a cart on a frictionless surface. Which of the following quantities is the same before and after the collision?
the momentum of the putty
the kinetic energy of the putty
the sum of the cart's and putty's momentum
the sum of the cart's and putty's kinetic energy
the momentum of the cart
8.Shari throws a ball of wet clay against a wall. The clay sticks to the wall after the collision. Which of the following is a correct statement about momentum in this collision?
The ball's momentum has been dissipated as heat.
This is not an elastic collision, so momentum is not conserved.
The wall is anchored to the earth, so the ball's loss of momentum is compensated for by an equal increase in the earth's momentum.
The ball's loss of momentum is compensated for by an equal increase in Shari's momentum.
The ball's loss of velocity is compensated for by a corresponding increase in the ball's mass in order to conserve momentum.
9.A 90 kg man jumps off the top deck of Yankee Stadium onto the net behind home plate 12 m below. His body experiences about half a ton (~ 5000 N) of force in the collision. About how much time elapsed between his initial contact with the net and when he came to rest?
0.03 s
0.0003 s
3 s
0.3 s
0.003 s
10.Two identical balls, each of mass 0.20 kg, sit on a low-friction table. Ball A moves toward stationary ball B at 1.4 m/s, as shown above. The balls strike a glancing blow, with ball B moving off after the collision at a speed of 0.30 m/s, at an angle of 30° below the x axis. What is the magnitude of the y component of ball A's momentum after this collision?
0.030 Ns
0.060 Ns
0.11 Ns
0.22 Ns
0.44 Ns