Practice problem: Momentum

NAME: _______________________

Do YOUR OWN WORK and SHOW ALL OF IT! (Continue on back, clearly labeled, if necessary)

This quiz does NOT require the use of a calculator. You may write answers as algebraic expressions (that is, write that x = 33.7 and y = 108.4, and that the answer is (x/y) kg m/s²). Trig functions and square roots may be left in that form (that is sin 25° or ).

All answers MUST include appropriate units and dimensions.

Ignore wind resistance and other sources of friction. (Assume acceleration is constant.)

1. For reasons that are not well understood by humans, any two dogs that see each other in a public place will run toward each other at high speed, colliding and bouncing without seeming to mind. For this problem, we will assume a 14 kg Big Dog collided with a 4 kg Little Dog after running toward each other along a straight line. We further assume that they bounced off of each other and moved away from each other along the same straight line (so they do not turn, and you may think of the collision as happening in one dimension). The velocities that the dogs had before the collision are given by the arrows in the diagram below, with the speeds indicated.

Immediately after the collision, the Little Dog went flying through the air to the right (the original direction of the Big Dog) with a speed of 10 m/s. You may assume that during the course of the collision, the only forces that were significant were the forces that the dogs exerted on each other.

a) Immediately after the collision, what was the velocity of the Big Dog?

(problem #1, continued)

b) Assuming that the forces that the dogs exerted on each other during the collision were great enough that other forces could be ignored, and assuming that the dogs were in contact with each other for one tenth of a second (0.1 seconds), what was the magnitude of the average force that the Big Dog exerted on the Little Dog?