The answers are being sorted out.

For B, firstly, the distance between them is not equal to the distance when they accelerate uniformly together and then stop.

As for why you don't want to wait, just think about it. After F exits, the front object will be pulled, and the back object will also be pulled. )

Therefore, a part of 2Ek energy must be converted into elastic potential energy b.

The force analysis of C shows that the friction force of the front object is different from that of the rear object. Obviously, the resultant force of b is greater than that of a.

C cuo

D impulse produces momentum change, and the momentum change is the same, so the impulse is the same.

For, one

Customer service combined with external force is to ask how much negative work to do with external force.

Obviously, the resultant force makes the energy of AB decrease continuously, and it is certain that the kinetic energy decreases to zero.

Using external force to do work will only reduce kinetic energy.

It turns out that both of them have the kinetic energy of Ek, and they share Ek respectively.

So the work that A adds up to is Ek.

Don't consider elastic potential energy when doing work with external force! !

Please add if you don't understand.