# physics

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To measure the height of a tree, you throw a rock directly upward, with a speed just fast enough that the rock brushes against the uppermost leaves and then falls back to the ground. If the rock is in the air for 2.1 s, how tall is the tree?

• physics -

If it is in the air 2.1 s, it takes 1.05 s (half the time) to return to Earth.

Solve the equation Height = (1/2)g t^2, with t = 1.05 s

g is the acceleration of gravity.

• physics -

5.4m

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