Consider a simple pendulum consisting of a small marble of mass 10 g that can be onsidered a point mass suspended from the lower end of an inextensible string of length 80 cm and whose mass is negligible. The upperstring is connected to a fixed point O .The pendulum is shifted by an angle 60º from its vertical position of equilibrium the string being stretched.

Question

a) Taking the level passing through A as reference level. Calculate the potential energy of the pendulum-earth system when the marble is at B. What is the mechanical energy of this system?

b) Mass m is released .Calculate neglecting all frictional forces the velocity of the marble when it passes through A.

Thanks.

Answer 1

and where is A, and B?

Answer 2

O
|\
| \B
|
A

Answer 3

A. The height of B is 80cm(1-cos60) PE is mgh
B. that pe becomes ke.
KE=mgh above
so 1/2 m v^2=mgh
v=sqrt(2gh) where h is the starting position height.