Answer to Question #86778 in Classical Mechanics for C

Question

After stealing a 20 kg bag of oranges, a 80 kg thief finds himself at rest on a frozen lake. He attaches himself to the bag of oranges with a long rope and pushes himself off from the bag by giving himself a rightward velocity. When the rope runs out:

A) both will move right because the thief has a larger kinetic energy
B) both will move right because the thief has a larger mass
C) both will move left because the thief has a larger kinetic energy
D) both will move left because the thief has a larger mass
E) both will stop

Answer 1

Initially, total momentum of the system (thief + oranges) is zero.

After the push, according to conservation of momentum principle total momentum is still zero, and so, after the rope runs out, two objects will stop.

Answer: E) both will stop