Energy and momentum - pendulums

[FrenchAtticus]

Homework Statement

A heavy ball swings on a string in a circular arc of radius 1m.
The two highest points of the ball's trajectory are Q and Q'; at these points the string is +/- 20 degrees from the vertical. Point P is the lowest point of the ball's trajectory where the string hangs vertically down. The acceleration of gravity is 9.8 m/s^2.

1.) What is the ball's speed at the point P? Neglect air resistance and other frictional forces.
2.) What is the magnitude of the ball's acceleration at the point P?
3.) What is the ball's speed at the point Q?
4.) What is the magnitude of the ball's acceleration at the point Q?

Homework Equations

mgh1 + 1/2mv1^2 = mgh2 + 1/2mv2^2

The Attempt at a Solution

9.8(1-cos(20)) + 1/2v1^2 = 0 + 1/2v2^2
0.591 + 1/2v1^2 = 1/2v2^2

How can I solve this with two unknowns?

 

[LowlyPion]

Why do you think there are 2 velocities to consider?

PE at highest = KE at lowest

m*g*h = m*v²/2