Force exerted on block B by Block A when being pushed on a frictionless surface

[yashboi123]

Homework Statement

Boxes A and B are in contact on a horizontal, frictionless surface (Figure 1). Box A has mass 25.0 kg and box B has mass 7.0 kg . A horizontal force of 100 N is exerted on box A \.

Relevant Equations

F = ma

I was just wondering why you would do
mB * a
to get the force A is exerting on B instead of
mA * a

 

[Cutter Ketch]

If B were not there, would there be any force on that side of A? If B was super small, would it take much force to keep it accelerating along with A? What if it was very large? So, you see, B’s inertia is the reason there is any force between B and A and B’s mass is what you need to figure out how big the force is.

 

[bob012345]

In problems like this always draw the free body diagrams and show the forces on each block separately. Then you can write the equations and they should makes sense.

 

[haruspex]

why you would do
mB * a
to get the force A is exerting on B instead of
mA * a

Because A's acceleration is a consequence of the two forces on A, whereas there is only one force on B.