Question

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

• A. Force of friction should be equal on the two walls.
• B. Force exerted by him on both walls should be equal and the walls should not be frictionless.
• C. He should press his feet with greater force.
• D. Coefficient of friction should be equal for both walls.

Answer 1

Answer: (B)

Force exerted by him on both walls should be equal and the walls should not be frictionless.

Answer 2

For equilibrium, the forces exerted by both walls on the man should be equal so as the horizontal forces may balance but the vertical forces can be balanced even if the forces of friction on the two walls are unequal.