Question

A person (40 kg) is managing to be at rest between two vertical walls by pressingone wall A by his hands and feet and the other wall B by his back (figure 6-E11). Assume that the frictioncoefficient 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. Take $g=10m/s^2$

Answer 1

Mass of man = 40 kg. g $=10m/s^2$
Frictional force developed between hands, legs and block side with the wall the weight of man. so he remains in equilibrium.
He gives equal force on both the walls so gets equal reaciton R from both the walls. If he applies unequal force R should be different the can't rest between the walls.

$\mu R+\mu R=40g\Rightarrow 2\mu R=40\times 10\Rightarrow r=\frac{40\times 10}{2\times 0.8}=250N$
The normal force = 250 N.