Two snooker balls, of the same mass, moving in opposite directions, collide head on. The pink ball is moving to the right at 5 m s1, the blue is moving at 3 m s1. The pink is brought to rest by the collision. (i) What is the velocity of the blue after the collision?
(ii) What is the change in momentum of each ball?
SAMPLE ANSWER 3B
Using the principle of conservation of momentum, making sure all values are in their standard unit and assigning a value on each direction (i.e. right is in the ‘’ direction and left is in the ‘’ direction): (i)
The velocity of blue after collision is 2 m s1 to the right.
(ii) Change in momentum of the pink is m1v1 m1u1 (m)(0) (m)(5) 5m. Change in momentum of the pink is 5m kg m s1 to the left. Change in momentum of the blue is m2v2 m2u2 (m)(2) (m)(3) 5m. Change in momentum of the blue is 5m kg m s1 to the right.
SAMPLE PROBLEM 3C
An 85 kg man collides head on with a 55 kg woman while the pair are skating in opposite directions on an ice rink.The two of them get tangled up in the collision and move off together after it. Given that the man has a speed of 8 m s1 and the woman 6 m s1,
(i) what speed do the pair move at after the collision?
(ii) If the man and woman had been travelling at right angles to each other before the collision, calculate their speed afterwards.
SAMPLE ANSWER 3C
(i) Using the principle of conservation of momentum, making sure all values are in their standard unit and assigning a value on each direction: m1u1 m2u2 m1v1 m2v2 m1u1 m2u2 (m1 m2)v
since the two bodies move off together after the collision v1 v2 v
