A bullet of mass m = 0.01 kg and velocity v0 = 21 m/s is fired toward a block of mass 4m. The block is initially at rest on a frictionless horizontal surface.

Question

A bullet of mass m = 0.01 kg and velocity v0 = 21 m/s is fired toward a block of mass 4m. The block is initially at rest on a frictionless horizontal surface.
The bullet penetrates the block and emerges with a velocity of 7 m/s.
(a) Determine the final speed of the block. (3) (b) Determine the loss in kinetic energy of the bullet. (3)
(c) Determine the gain in the kinetic energy of the block. Then calculate the overall loss in kinetic energy. What form of energy is this energy loss? (6)

oobleck · Answer

(a) conserve momentum. 0.01*21 = (0.01+4)v (assuming a "mass 4m" is really 4 kg) (b,c) KE = 1/2 mv^2, so ...