(a) A ladder stands on a horizontal surface (the floor) and leans against a vertical wall. Suppose a ladder of length l =3.04 m with mass m1 = 13.3 kg, rest against a smooth wall at an angle of =24.8o with the wall. A student, who has a mass ms= 62.0kg, stands on the ladder. The student is standing on a rung that is r = 1.43 m along the ladder, measured from where the ladder touches the ground.

What friction force must act on the bottom of the ladder to keep it from slipping? Neglect the small force of friction between the smooth wall and the ladder.