Question

During a game of marbles, a player is trying to win a 2 g marble that is at rest. The player flicks a 1.25 g marble at a velocity of 8 at the larger marble that is sitting still. After the collision, the smaller marble has a velocity of 1 . What is the velocity of the 2 g marble after the collision? Round your answer to the nearest whole number.

Answer 1

Use conservation of momentum (no external forces):

m1 v1i + m2 v2i = m1 v1f + m2 v2f

So v2f = m1(v1i − v1f)/m2. Using m1 = 1.25 g, m2 = 2 g, v1i = 8 m/s, v1f = 1 m/s:

v2f = (1.25(8 − 1))/2 = (1.25·7)/2 = 8.75/2 = 4.375 m/s ≈ 4 m/s.