Question

A block of mass m is kept over another block of mass $M$ and the system rests on a horizontal surface. A constant horizontal force $F$ acting on the lower block produces acceleration $\frac{F}{2(m+M)}$ in the system, the two blocks always move together. Find the work done by the force of friction on the smaller block by the bigger block during a displacement d of the system.

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Given $a$ = $\frac{F}{2(m+M)}$

$\therefore Netforceonm=ma$

= $\frac{mF}{2(M+m)}N$

This should the magnitude of friction forces acting on m as there are no other horizontal forces.

$\therefore Workdone=f.scos\theta$

$=\frac{mF}{2(M+m)}xdxcos{0}^{\circ }$

$=\frac{mFd}{2(M+M)}$