Classical Mechanics - Pendulum

Which of the following best illustrates the acceleration of a pendulum bob at points a through e?

(GR0177 #01)

Solution:

The acceleration of pendulum: a = a_centripetal + a_tangential
a_cent = v²/r = ω²r
a_tan = αr

At equilibrium (position B): ω = constant
α = dω/dt = 0
a = a_cent

At maximum amplitude (position A and C): v = 0
a = a_tan

At other positions:
a = a_cent + a_tan

Answer: C