Question

Shelly rolls ball A in the positive x direction with a velocity of
7.5 meters/second. It hits stationary ball B and they undergo elastic collision. The two balls have different masses. Which of the following statements is true?


answers:
A. the sum of their X-momentum must be equal to zero?
B. the sum of their Y-momentum must be equall to zero?
C. the sum of their X-velocities must be equall to zero?
D. the sum of their Y-velocities must be equall to zero?