Monday, April 11, 2011

How far will a freely falling object fall from rest in five seconds?

Hello!


I suppose we speak about falling near Earth's surface and that the air resistance is ignored (in practice, it cannot be ignored).


Then the only force acting on a body is the gravity force. It may be considered constant near the surface. By Newton's Second law a constant force gives a body a constant acceleration: a=F/m. Actually this acceleration doesn't dependent on a body's mass and equal to 9.8 `m/s^2.` It is usually denoted as g.


A constant acceleration makes uniformly increasing speed, V=gt, and a displacement `D=(g t^2)/2.`  Here t is a time from the start (in seconds), and the fact that a body starts from rest is already taken into account.


This way, t=5s and `D=(g*t^2)/2 approx 122.5 m.`  This is the answer.

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