Answer
a). Diagram is as shown.
It is the force of static friction acting on bottom surface of A due to top surface of B that is responsible for A's acceleration.
So, option (4) is correct answer.
b). $F_{A}=m_{a}\times a=2\times2.5=5N$
$F_{B}=m_{b}\times a+F_{A}=5\times2.5+5=17.5N$
Work Step by Step
a). Diagram is as shown.
It is the force of static friction acting on bottom surface of A due to top surface of B that is responsible for A's acceleration.
So, option (4) is correct answer.
b). $F_{A}=m_{a}\times a=2\times2.5=5N$
$F_{B}=m_{b}\times a+F_{A}=5\times2.5+5=17.5N$
