Question

A ball is dropped from rest from the top of a building and takes 3.5s to hit the ground. Calculate the speed at which the ball hits the ground.

Answer 1

Answer:

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$t = \frac{u}{g} \\ t = time \: of \: flight\\ 3.5 = \frac{u}{10} \\ u = 35m {s}^{ - 1}$

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$h = \frac{ {u}^{2} }{2g} \\ h = \frac{35 \times 35}{2 \times 10} \\ h = 61.25m$

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$v = \sqrt{2gh} \\ v = \sqrt{2 \times 10 \times 61.25} \\ v = \sqrt{1225} \\ v = 35m {s}^{ - 1}$