Tangential Acceleration of a Pendulum

1. Jul 2, 2009

Sandman327

1. The problem statement, all variables and given/known data
A 2kg pendulum bob on a string 2 meters long is released with a velocity of 1.5 meters/second when the support string makes an angle of 30 degrees with the vertical. What is the tangential acceleration of the bob at the highest point of its motion? The answer was given as 5.77 meters/second squared so I know that that is the answer but it's getting to that number that is giving me tons of trouble.

2. Relevant equations
Tangential acceleration = r(delta omega/change in time)

3. The attempt at a solutionI have an FBD and the only force acting on the bob is gravity. However the problem I'm having is that I am almost positive there is another equation I should be using but I'm not sure what it is or what I should try to solve for. Time? Maximum height? both?

2. Jul 2, 2009

LowlyPion

Consider the total energy of the system.

They give you the kinetic energy. You have the potential energy from gravity with reference to how high it is from the bottom. So figure the maximum height first, and then figure what angle that makes, and that angle to gravity is the fraction of gravity which is the tangential acceleration I think they are looking for.