Two balls of identical sizes but different masses moving exactly along the same straight line. The left ball (m = 0.5 kg) is moving with a velocity of 2 m/s to the right, and the right ball (m = 0.1 kg) is moving at 0.25 m/s to the right also. The balls collide. After the collision, the velocity of the right ball is 1.5 m/s to the right.

Question

Two balls of identical sizes but different masses moving exactly along the same straight line.  The left ball (m = 0.5 kg) is moving with a velocity of 2 m/s to the right, and the right ball (m = 0.1 kg) is moving at 0.25 m/s to the right also.  The balls collide.  After the collision, the velocity of the right ball is 1.5 m/s to the right.

1.  What is the kinetic energy in J of the left ball after the collision?

bobpursley · Answer

conservation of momentum:
.5*2+.1*.25=.5V+.1*1.5
1+.025-.15=.5V
V=2(.875)=1.75 m/s to right (which is impossible, of course as it had to just go through thr right ball going slower.
KE= 1/2 m v^2=1/2 *.5*1.75^2 J