Question

A force of $100$N is applied on a block of mass $3$ kg as shown in the figure. The coefficient of friction between the wall and block is $0.6$. The magnitude of the force exerted by the wall on the block is?

• A. $15$N downwards
• B. $25$N upwards
• C. $20$N downwards
• D. $30$N upwards

Answer 1

The correct option is C $20$N downwards

The force is acting on the body in 30 degree perpendicular to the wall.

From the free body diagram we can resolve that,

$100cos{30}^0+F=30N$

$F=30-100\times \frac{1}{2}=-20N$

Hence the magnitude of force exetred by the wall is $20N$ downward