Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Some Easy Momentum Problems

  1. Mar 29, 2010 #1
    1.1. A 7 kg glider on an air track starts with an initial velocity of 32 m/s and then runs into a 2 kg glider which is initially at rest. During the collision, which glider has a larger magnitude change in momentum? Explain your answer.

    2. We observe the center of mass of a system of objects and realize that it is accelerating. Could all of the forces acting on the system be internal forces? Why or why not?

    3. You are playing pool. You hit the cue ball into the 6 ball. If there is no spin on the ball and you hit it straight on center, the cue ball stops dead, and the 6 ball rolls off with approximately the same velocity that the cue ball had before. Is the collision between the balls:

    Almost completely elastic
    Almost completely inelastic
    Roughly halfway between completely elastic and completely inelastic
    You can't tell from the information given.

    4. Explain your answer to the multiple choice question

    2. Relevant equationsK=(1/2)mv^2

    3. 1. They both experience the same magnitude change, since this is an isolated system, and these two objects exert the same force on each other (in magnitude, but opposite directions, according to Newton's 3rd law).

    2. No, if all the forces acting on it were internal, then net force would equal zero, and there would be no acceleration. Thus, there must be some external forces.

    3. Almost completely elastic

    4. In this example, the total kinetic energy would be the same after the collision, as before the collision. Before the collision, one of the balls is moving with a certain velocity, and one is at rest. After the collision, the other ball has started moving with the same velocity, while the other one is now at rest. The balls are of roughly equal mass, and thus, the initial total kinetic energy is equal to the final total kinetic energy.

    Thanks for any help!!!
  2. jcsd
  3. Mar 30, 2010 #2
  4. Mar 31, 2010 #3
    Bump again.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook