- A 14 kg rock starting from rest free falls through a distance of 5.0 m with no air resistance. Find the momentum change of the rock caused by its fall and the resulting change in the magnitude of earth’s velocity. Earth’s mass is 6.0 × 10
^{24}kg. Show all your work, assuming the rock-earth system is closed.

Guest Jan 29, 2020

#1**+5 **

Assuming the rock is near enough to the surface of the Earth that we can take its acceleration to be g (=9.81m/s^{2})' then we can get its velocity at 5m from v_{rock} = sqrt(2*9.81*5)m/s, and its momentum as m_{rock }* v_{rock }(since it starts from rest).

To get Earth's change in velocity use m_{Earth}*v_{Earth} = -m_{rock}*v_{rock}

Alan Jan 29, 2020