Question

In the picture shown below, the man is

(A) Applying no force on the stool
(B) Applying pressure on the stool
(C) Applying force on the stool
(D) Both (B) and (C)

Answer 1

Hint : To solve this question, we need to use Newton's second and the third laws of motion. For that we have to consider the free body diagram of the man. From there we get the equation of motion of the man and can calculate the pressure exerted by the man on the stool.

Complete step by step answer
Let the mass of the man be $m$ .
We know that the earth attracts each body with a gravitational force acting vertically downwards. The force is given by
$\Rightarrow W = mg$
Also, as the man is sitting on the stool in a state of rest. So this means that the man is in equilibrium. To keep him in the state of equilibrium, there must be a force applied on him which should equal and opposite to the force of gravity. We know that this force is the normal force applied by the stool. So, we consider the free body diagram of the man as shown in the figure below.

From the free body diagram of the man, we have
$\Rightarrow N = mg$ (1)
As the stool is applying a normal force equal to the weight of the man, so according to Newton's third law of motion, the man will exert a force of reaction on the stool equal in magnitude and opposite in direction to the normal force.
Thus, the man is applying force on the stool.
So option C is correct.
Now, the pressure on a surface is defined as the force acting on the surface normal to it per unit area of the surface. Let the surface area of contact of the man and the stool be $A$ . From (1) the normal force on the stool is equal to $mg$ . So the pressure applied by the man on the stool is given by
$\Rightarrow P = \dfrac{{mg}}{A}$
Therefore the man is applying pressure on the stool.
So the option B is also correct.
Thus both the options B and C are correct.
Hence, the correct answer is option D.

Note
We should not misunderstand that the force of gravity is the force applied by the man on the stool. The force of gravity is the force applied by the earth on the man. The force which is applied on the stool is the normal force, which comes out to be equal to the weight of the man.