Problem 7-51 Energy cons.

A boy is playing with a rope tied to a tree near his favourite swimming hole. Initially the boy is stationary and the rope (of length $3.7 \;m$) makes an angle of $48^\circ$ with the vertical. He then lifts his feet slightly and starts to swing freely. If air resistance is neglected, use conservation of energy to determine:

(a) his speed at the bottom of the swing
(b) the minimum height, relative to his initial position, to which he can swing.

Where should the origin be chosen in this problem?

(A)   Where the motion starts, i.e. at 1 in the drawing.

(B)   At the bottom of the swing, i.e. at 2 in the drawing.

(C)   At the top of the rope.