Momentum and rotation [1] Two objects collide and stick together afterward. In s

Question

Momentum and rotation
[1] Two objects collide and stick together afterward. In such an interaction,

(a) mechanical energy is NOT conserved. (b) momentum is NOT conserved.
(c) kinetic energy is conserved. (d) both a and b. (e) none of the above.

[2] A red cart of mass 1.0 kg collides with a stationary blue cart of mass 0.25 kg. The change in momentum for the blue cart, compared to that for the red cart,
(a) is equal and opposite. (b) is four times as large. (c) is twice as large.

(d) is the same. (e) depends on whether the collision is elastic or inelastic.

[3] Two particles collide head-on. (1 dimensional) In the center of mass frame, the total final momentum is

a) zero for all collisions. b) zero only for completely inelastic collisions. c) equal to the total initial momentum in the lab frame.
d) equal to minus the total initial momentum in the lab frame.
e) none of these.

[4] In a one dimensional perfectly elastic collision, the total kinetic energy in the center of mass frame _________ the total kinetic energy in the lab frame.
a) is less than b) is greater than c) is equal to

d) may be greater than or less than but not equal to e) Can be any factor times

[5] For perfectly elastic, one dimensional collisions in the center of mass frame, the final velocities of the two objects are equal to
a) the negative of the initial velocities because the center of mass must remain stationary. b) the initial velocity of the other mass because they exchange motions.

c) the negative of the initial velocities because the kinetic energy of each must be constant.

d) negative the initial velocity of the other mass because they exchange motion and change direction.
e) none of these.

[6] Two disks of radius 2 cm. collide elastically and off-center. The final velocity components which are perpendicular to the line between centers at contact are

a) equal to negative their initial values. b) the same as before collision.

c) equal to the initial component of the other disk. d) zero. _______________________________________________________________________

[7] Two carts of equal mass move on a frictionless track. The red cart is initially at rest and the blue cart approaches it at 0.25 m/s. The velocity of the red cart after a perfectly elastic collision is how many times as large as the velocity after a totally inelastic collision (with data as above)?

(a) 12 (b) 1 (c) 2 (d) 0

Explanation / Answer

1. (a) mechanical energy is NOT conserved.

2. (a) is equal and opposite.

3. c) equal to the total initial momentum in the lab frame.

4. c) is equal to

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