# With what speed does the rock hit the bottom?

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A rock released from rest to fall on a small airless planet falls #y=g t^2# m in #t# sec, #g# a constant. Suppose that the rock falls to the bottom of a crevasse #"20 m"# below and reached the bottom in #"4 sec"# .

With what speed does the rock hit the bottom?

A rock released from rest to fall on a small airless planet falls

With what speed does the rock hit the bottom?

##### 1 Answer

Oct 17, 2017

#### Answer:

5 m/s

#### Explanation:

also on a small airless planet, the second movement law say:

therefore, knowing y = 20 m and t= 4 s I can calculate the aceleration:

now from the first law we have