Posted by Brianna on Sunday, November 14, 2010 at 12:03pm.
A stone was thrown into the air and returned after 4.2 seconds.
a) At what speed was the stone thrown? (20.6) < i got that right.
b) How high did the stone go? (21.6 m)
i don't know how to get b. what steps do i do?

Physics  Free Fall  MathMate, Sunday, November 14, 2010 at 2:31pm
The stone with an initial velocity, v, has a kinetic energy of (1/2)mv².
When at the top, velocity = 0, but the potential energy is mgh.
So equate energies to get
mgh = (1/2)mv²
Solve for h.
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