a When the carts are in the hold part of the PullHoldRelease

[a.] When the carts are in the \"hold\" part of the Pull-Hold-Release sequence, the acceleration is zero. Is the force on cart B that is exerted by the string connected to the hanging weight equal in magnitude to the force on cart B exerted by the string from cart A? Would these forces be examples of a \"third-law pair\"? Answer the question of whether these force during the hold have the same magnitude, and explain why or why not they would be third law pairs.

[b.] Why are different magnitudes of force measured during the \"release\" part of the sequence for different weight distributions between the carts (that is, one bar on each cart, both bars on cart A or both bars on cart B), as recorded in the table in step 2.7?

Pull and hold, then release Cart B Cart A Hanger

Solution

a)

Yes, the force on B that is exerted by the string connected to the hanging weight equal in magnitude to the force on cart B exerted by the string from cart A.

As these are the only forces in the direction of motion and the acceleration is 0. So, the forces must be equal.

But these are not action-reaction pairs and thus are not examples of third law pair.

This is due to the fact that these forces do not act at the interface of the action of two bodies. three bodies are involved in this case

b)

It is due to the fact that as the number of bars are added, the mass changes and the force required to keep accelerated also changes.

If two bars are added to the cart A, the tension which pulls the cart A must be greater so as to make up for the same acceleration when the bars are kept on both the carts.