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  1. 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 × 1024 kg. Show all your work, assuming the rock-earth system is closed.
 Jan 29, 2020
 #1
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Assuming the rock is near enough to the surface of the Earth that we can take its acceleration to be g (=9.81m/s2)' then we can get its velocity at 5m from vrock = sqrt(2*9.81*5)m/s, and its momentum as mrock * vrock (since it starts from rest).  
 

To get Earth's change in velocity use mEarth*vEarth = -mrock*vrock

 Jan 29, 2020
edited by Alan  Jan 29, 2020

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