Question

Coefficient of friction between $A$ and $B$ is $\mu$. The minimum force $F$ with which $A$ will be pushed such that $B$ will not slip down is

• A. $\frac{M g}{\mu}$
• B. $\frac{m g}{\mu}$
• C. $\frac{(M+m) g}{\mu}$
• D. $\frac{(M-m) g}{\mu}$

Answer 1

Answer: (C)

From the reference frame of $A$
$\mu N=m g$
$N=m a$
$N=m\left(\frac{F}{M+m}\right)$
$\mu m\left(\frac{F}{M+m}\right)=m g$
$F=\left(\frac{M+m}{\mu}\right) g$