Lucy and Julie are stationary and on roller skates. They are connected by a rope. When Lucy pulls the rope,
A. Only Lucy moves
B. Only Julie moves
C. No one moves
D. Both move

Question

Lucy and Julie are stationary and on roller skates. They are connected by a rope. When Lucy pulls the rope,
A. Only Lucy moves
B. Only Julie moves
C. No one moves
D. Both move

anonymous · Answer

Assuming that there is no significant friction (because of the roller skates):

Lucy applies a force on the rope causing Julie to feel a tension force towards Lucy. This force would cause Julie to begin to accelerate towards Julie. However, there is an equal and opposite tension force when Lucy pulls the rope, towards Julie. 

This reaction force would cause Lucy to also begin accelerating towards Julie.

Therefore they both end up moving