Question

A man tries to remain in equilibrium by pushing with his hands and feet against two parallel walls. For equilibrium, 

(a) he must exert equal forces on the two walls 

(b) the forces of friction at the two walls must be equal 

(c) friction must be present on both walls 

(d) the coefficients of friction must be the same between both walls and the man

Answer 1

Correct Answer is: (a, c)

The horizontal forces on the man must balance, i.e., the forces exerted by the two walls on him must be equal.

The vertical forces can balance even if the forces of friction on the two walls are unequal. The torques due to the forces of friction about his centre of mass must balance. This requires friction on both walls.