A rock falls from the top of a cliff onto a roadway below. It takes 2 s to fall and its speed when it hits the road is 20 m/s. Assume no air friction, what acceleration does gravity give the rock as it falls?

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Answer 1 · 2018-01-17T19:25:38

#10#m/#s^2#

before the rock starts to fall, it is at rest.

this means that its starting velocity is #0# m/s.

we are given that the final velocity is #20# m/s.

the rock's velocity goes from #0# m/s to #20# m/s, over #2#s.

equation for acceleration: #a = (v-u)/t#

#v - u = 20-0#

#(20-0)/2 = 20/2#

#a = 10# m/#s^2#

this acceleration is due to gravity, since the resultant force acting on the rock, and causing it to fall, is in a downward direction.