A person ( 40 kg ) manages to remain at rest between two vertical walls by pressing one wall A with his hands and feet and the other wall B with his back. The friction coefficient between his body and the walls is 0.8 , and limiting friction acts at all contact points. Determine the normal force exerted by either wall on the person. Take g = 10 m/s ^2 .

Step-by-step solution

Let the normal force exerted by wall A on the person be N_A and by wall B be N_B . For horizontal equilibrium, the net horizontal force on the person must be zero. Therefore, the normal forces exerted by the two walls must be equal: N_A = N_B = N For vertical equilibrium, the total upward frictional force must balance the downward weight of the person. The weight of the person is W = mg = 40 10 = 400 N . Since limiting friction acts at all contact points, the frictional forces at walls A and B are: f_A = N_A = N f_