Question

a 4 kg block A is placed at the top of 8 kg block B which rests on a smooth surface.A just slips on B when a force of 20N is applied on A. The maximum horizontal force F required to make both A and B move together​

Answer 1

Answer:

180 newton is right answer

Answer 2

F= 60N

Explanation:

If the both blocks A and B move together then the acceleration will be same. If f is the force of friction between A and B .

Then,

$F-f=m_b\times a$  and $f= m_a\times a$

So $a=\frac{f}{m_a}=\frac{20}{4}=5m/s^2$

so$F-20=8\times 5=40$

F= 20+40=60N

F= 60N