A hailstone falls from a height of 5 km. Ignoring air resistance, what is the hailstone's final velocity? The acceleration due to gravity is 9.8 ms−2.

1 Answer
David G.
May 9, 2016

If we assume no air resistance the velocity is given by:

v2=u2+2ad and u=0, so, rearranging:

v=√2ad=√2⋅9.8⋅5000=313 ms−1 or about 1127 km−1

Explanation:

In order to answer this question it is necessary to assume that air resistance does not act. This is not a very realistic assumption.

Any real object falling has a 'terminal velocity' at which the air resistance acting upward balances the gravitational force acting downward. At that velocity, there is no further acceleration.

For a human skydiver this velocity is about 56 ms−1 or 200 kmh−1. A hailstone is both smaller and lighter, so it is hard to guess its terminal velocity, but it would be less than 313 ms−1.

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