The pendulum shown to the left consists of a bob of mass of 0.35 kg, attached to a string of lengthL= 1.1 meters. It is moving to the right with a speed of 4.64 m/sec at point A. What we'd like to know is what the the velocity of the bob when it reaches point B which is 38 degrees from vertical.
There are two different ways to look at this problem, each of which will give us the same answer. Let's look at each separately. (For all of the questions below, let's start by defining the potential energy of the bob to be zero at point A.)
First, lets look at the question in terms of the work energy theorem. (WTOT= ---> KE) What is the work done by on the bob by gravity as it moves from point A to point B?
WGRAV=