Two identical low-friction carts, Cart A and Cart B
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
Two identical low-friction carts, Cart A and Cart B, rest on a horizontal track. A third cart, Cart C, of different mass is positioned nearby but never touches the other carts. A spring-loaded plunger on Cart A is released, causing Cart A to move to the right and collide with Cart B, which is initially at rest. Cart C remains motionless throughout the event.
Assume all wheels are nearly frictionless and air resistance is negligible.
(a) Describe, in words, the criteria you would use to decide which objects must be included in the system if you wish to treat the total linear momentum as conserved during the collision.
(b) Using the criteria you described in part (a), identify all objects that belong in the momentum-conserving system for this scenario and justify your choice.
(c) Suppose the track is not perfectly horizontal but instead slopes gently downward to the right so that a constant component of the carts’ weight acts along the track. Explain qualitatively how this would affect the validity of treating the total linear momentum of the system you chose in part (b) as constant during the collision.