The bob describes vertical circular motion :

But net force along the string is T - mgcos a, which must act as the centripetal force.

Now, as the bob moves on the arc of a circle from H to P its speed increases from zero to vp and its Potential energy (P.E.) decreases from mgl to mg(l - h)

\    gain in Kinetic energy (K.E.)   =   loss in P.E.

Index

2.1 Definitions
2.2 Motion in one Dimension
2.3 Motion in two Dimension

Chapter 3