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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