Question

In the figure shown below, what is the minimum weight of block B that will remain at rest as a horizontal force P starts motion of block A which weights $300N$? (The angle of friction is ${15}^{\circ }$ between A & B while the coefficient of friction is $0.3$ between B and the ground)

• A. 700

Answer 1

The correct option is A 700

F.B.D of block A

Force diagram for block 'A'

Applying Lami's theorem:

$\frac{300}{sin45}=\frac{R_A}{sin90}=\frac{P}{sin45}\Rightarrow R_A=424.26N$

Now draw F.B.D for block B

$\Phi =ta{n}^{-1}\left(0.3\right)={16.7}^{\circ }$

Force diagram for block B


$\frac{424.26}{Sin16.7}=\frac{W_B}{sin28.3}$

$\therefore W_B=699.94N=700N$