A pendulum with cord length L = 6 ft and a bob weighing 3 lb is released from rest at an a...

A pendulum with cord length L = 6 ft and a bob weighing 3 lb is released from rest at an angle θi. Once the pendulum has swung to the vertical position (i.e., θ = 0), its cord runs into a small fixed obstacle. In solving this problem, neglect the size of the obstacle; model the pendulum’s bob as a particle and the pendulum’s cord as massless and inextensible; and let gravity and the tension in the cord be the only relevant forces.

Figure P3.71

What is the maximum height reached by the pendulum, measured from its lowest point, if θi = 20°?