A 3-kg mass is attached to a light string of length 1.5 m to form a pendulum. The mass is given a initial speed of 4 m/s at its lowest position. When the string makes and angle of 30° with the vertical, find (a) the change in potential energy of the mass, and (B) the speed of the mass (c) What is the maximum height reached by the mass above its lowest point?
The Attempt at a Solution
I was able to solve and get correct all parts of this problem except (a).I attempted to find the answer by finding the total energy using KE=1/2mv^2. I found the total energy to be 24 J. Then I found the height of the pendulum at 30 degrees by doing 1.5 cos 30°. Then I subtracted that value from 1.5 to find the height. I then did 3(9.8)(.2) to find the change in potential energy. I got 5.88 and the books answer says its 5.91 J.