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PLEASE HELP (question) A 100 kg rock sits on top of a 80-meter cliff. If the rock falls, how fast is it going at 20 m? Ignore air resistance.
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PLEASE HELP

(question) A 100 kg rock sits on top of a 80-meter cliff. If the rock falls, how fast is it going at 20 m? Ignore air resistance.

User Greg Tarsa
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y = v0t + 1/2gt^2.
v0 is 0 as it is at rest initially. So now we have y=1/2gt^2 so 60=1/2(9.8)t^2 and we must solve for t. t= about 3.5 seconds. Since the acceleration is 9.8 m/s^2 we do 9.8 m/s^2 times 3.5 seconds to get 34.3 m/s.
User Steve Sawyer
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