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A small rock is thrown vertically upward with a speed of 17.0m/s from the edge of the roof of a 26.0m tall building. The rock doesn't hit the building on its way back down and lands in the street below. Air resistance can be neglected.

Part A

What is the speed of the rock just before it hits the street?

Part B

How much time elapses from when the rock is thrown until it hits the street?

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Assume the acceleration due to gravity is 9.81 m/s^2

v^2 = u^2 + 2as

v^2 = 17^2 + 2 * 9.81 * 26
= 799.12

The velocity (v) just before the rock hits the ground is
root(799.12) = 28.2687 m/s (to 3 decimal places).

v = u + at

28.2687 = -17 + 9.81t

The tiime that the rock is in flight is
t = 45.2687 / 9.81 = 4.614 seconds (to 3 decimal places).
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