5-55. The exercise machine consists of a rigid bar, pin connected to the frame at A. As the man pushes up on the bar it stretches the rubber band BC. If the stiffness of the

rubber band is k = 500 lb/ft, determine the applied vertical

force F needed to hold the bar in the position 0 = 30°. The rubber band is unstretched when 0 = 0°.

• 5 ft

0.5 ft

C

Prob. 5-55