A 38 g ball is fired horizontally with initial speed v0 toward a 100 g ball that
ID: 2305249 • Letter: A
Question
A 38 g ball is fired horizontally with initial speed v0 toward a 100 g ball that is hanging motionless from a 1.1m long string. The balls undergo a head on perfectly elastic collision, after which the 100 g ball swings out to a max angle=51°. What was the initial velocity v0? A 38 g ball is fired horizontally with initial speed v0 toward a 100 g ball that is hanging motionless from a 1.1m long string. The balls undergo a head on perfectly elastic collision, after which the 100 g ball swings out to a max angle=51°. What was the initial velocity v0?Explanation / Answer
Gain in potential energy of the suspended ball:
U = mgh = mg[L - Lcos51]
=> U = 0.1 x 9.8 x 1.1[1 - cos51] = 0.4 J
since the collision is elastic, this must be the kinetic energy of the striking ball
so, 0.4 = (1/2)mvo2
=> vo = 4.588 m/s.
this is the initial velocity of the striking ball.