Question

a block A of mass4 kg is placed on another block B of mass 5kg B rests on smooth table for sliding block A onB a horizontal force of 12 N is required to be applied on A how much max force can be applied on Bso that both A andB move together

Answer 1

Hello there

In order for the forces to be balanced the resultant  force needs to be zero. Since A and b are place on top of each other the combined weight is 8 kg and in order for the forces to be balanced an equal force needs to be applied.

I hope this answers your question

Thanks

Answer 2

When the blocks move together the acceleration will be same.  block A = mass4 kg and If f is the force of friction between A and B

F- f = mb-a  

And f = maa...  

So a = f/ma = 12/4 = 3m/s2

so F-12 = 8*3 = 24

F = 12+24 = 36N