Question

In the figure, a block of weight $60 \,N$ is placed on a rough surface. The coefficient of friction between the block and the surfaces is $0.5$. What should be the weight $W$ such that the block does not slip on the surface?

• A. $60\,N$
• B. $\frac{60}{\sqrt{2}}N$
• C. $30\,N$
• D. $\frac{30}{\sqrt{2}}N$

Answer 1

Answer: (C)

Frictional force:
$F=\mu \,R = 0.5 \times mg $
$= 0.5\times 60=30\,N$
Now $F=T_{1}=T_{2}\, cos\,45^{\circ}$
or $30=T_{2}\,cos\,45^{\circ}$
and $W=T_{2}$ $sin\,45^{\circ}$
Solving them we get $W=30\,N$