Question

A stand shows a pendulum in 5 positions. A has the pendulum bob at a 45 degree angle to the left. C has the pendulum bob straight down, and B is halfway between A and C. E is has the pendulum bob at a 45 degree angle to the right, and D is halfway between C and E.
Determine how potential and kinetic energy changes at each position of the pendulum as the ball swings from A to E.

Position A:
is all potential

Position B:
is losing potential and gaining kinetic

Position C:
is all potential

Position D:
is all potential

Position E:
is losing kinetic and gaining potential

Answer 1

You're close, but a few positions were mislabeled. Assuming no friction and choosing the lowest point (C) as the reference for minimum potential energy, energy transforms like this as the bob swings A → C → E:

- A (left extreme, 45°): all potential energy, KE = 0 (velocity = 0), U is maximum.
- B (halfway between A and C): U is decreasing and K is increasing (some potential converted into kinetic).
- C (bottom, vertical): K is maximum and U is minimum (most of the energy is kinetic).
- D (halfway between C and E): K is decreasing and U is increasing (kinetic converting back into potential).
- E (right extreme, 45°): all potential energy again, KE = 0, U is maximum.

Total mechanical energy (U + K) stays constant throughout (neglecting friction/air resistance).