april is about to release the bob of a pendulum.?

Question

before she lets go, what sort of potential energy dose the bob have? how dose the energy of the bob change as it swings through one full cycle of motion?

Answer 1

Potential energy Pe=
Pe = mgh
m- mass of the bob
g- acceleration due to gravity
h - height above the lowest point of the bob's center of gravity swing

Kinetic energy Ke
Ke= .5 mv^2
v - velocity of the bob

h= L- Lcos (A)
v= LA (A in radians in this case)
L - length of the string
A- pendulum's starting angle

Energy of the bob as it swings
E=Pe+Ke
E= mg( L- Lcos (A)) + 0.5 m(LA)^2

Note Ke=o at angle +/- a and Pe =0 when the bob is at its lowest point of the swing.