With what speed does the rock hit the bottom?

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?

1 Answer
Oct 17, 2017

Answer:

5 m/s

Explanation:

also on a small airless planet, the second movement law say:
# y=1/2 at^2#
therefore, knowing y = 20 m and t= 4 s I can calculate the aceleration:
#a= (2y)/t^2=20m/(4s)^2= 1,25 m/s^2#
now from the first law we have# v= at = 1,25 m/s^2 xx 4 s= 5m/s#