- #1

NoobeAtPhysics

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## Homework Statement

This problem has analogies in the game of pool. Puck 1 slides on a horizontal, frictionless surface with velocity v and collides elastically with stationary puck 2; each puck has the same mass, m. The pucks move off with velocities v1 and v2, as shown. The angles θ1 and θ2 are measured relative to the initial direction of puck 1.

Which of these statements is correct?

1) v^2 = v1^2+v2^2

2) This problem has analogies to pool because pool balls have equal mass and roll without friction. [As long as rotational KE of pool balls is neglected, the analogy is perfect.]

3) In this problem, linear momentum is conserved but kinetic energy is not conserved.

4) 0 = v1sinθ1−v2sinθ2

5) If b+c = a for three non-zero vectors, and b^2+c^2 = a^2, then the angle between a and c is 90°.

## Homework Equations

mv1 + mv2 = mv1' + mv2'

## The Attempt at a Solution

1) False

2) True

3) False

4) False

5) True

Thinking why Im wrong here, maybe it is number 1? Using the momentum formula, I find that v1 = v1' + v2', not the equation described.

best regards,

Noobe

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