Question

A person $\left(40kg\right)$ is managing to be at rest between two vertical walls by passing one wall $A$ by his hands and feet and the other wall $B$ by his back. Assume that the friction coefficient between his body and the walls is $0.8$ and that limiting friction acts at all the contacts.
(a)Show that the person pushes the two walls with equal force.
(b)Find the normal force exerted by either wall on the person.

Answer 1

(a) The man pushes both walls, in turn the wall also pushes him in equal and opposite directions considering the horizontal forces in horizontal direction on the man, only the normal force by walls be Rand $R^{\prime }$.

Then $R=R$ at equilibrium

Hence, the man pushes both walls with equal forces, and friction forces on both walls are also equal.

(b) Weight of man $=40kg=400N$.

In vertical direction $2F=400$ or $F=200N$

Also, $F=\mu R$

or, $200=0.8R$

$\therefore R=250N$