Question

Two blocks of masses m and 2 m placed one over the other as shown in figure. The coefficient of friction between m and 2m is µ and between 2m and ground is $\frac{\mu }{3}$. If a horizontal force F is applied on upper block and T is tension developed in string then choose the incorrect alternative.

• A. If $\text{F}=\frac{\mu }{3}\text{mg},\text{T}=0$
• B. If $\text{F}=\mu \text{g},\text{T}=0$
• C. If $\text{F}=2\mu \text{mg},\text{T}=\frac{\mu \text{mg}}{3}$
• D. If $\text{F}=3\mu \text{mg},\text{T}=0$

Answer 1

The correct option is C

If $\text{F}=2\mu \text{mg},\text{T}=\frac{\mu \text{mg}}{3}$

$f_{1_{\text{max}}}=\mu \text{mg}$

$f_{1_{\text{max}}}=\frac{\mu }{3}\left(3\text{mg}\right)=\mu \text{mg}$

$T=0\Rightarrow$ Tension will be zero in all circumstances is zero.