How Fast Does a Rock Fall from 20 Meters?

[McNutt74]

Homework Statement

A rock with a mass of 0.2 kg is dropped from a height of 20 m. At what velocity does the rock strike the ground?

Homework Equations

KE= 1/2mv^2
PE=mgh

The Attempt at a Solution

0.2x9.81x20=1/2mv^2.
39.24=.1(v^2)
392.4=v^2
v=19.8 m/s
First time doing one of these problems, does my answer seem reasonable and did I use the right set of equations for this particular problem and did i set it up right? Thanks

 

[gneill]

First time doing one of these problems, does my answer seem reasonable and did I use the right set of equations for this particular problem and did i set it up right? Thanks

Looks good. Well done.

Note that if you'd done the math symbolically first (before plugging in any numbers) you could have saved some arithmetic:

1/2mv^2 = mgh

Note that the "m" cancels on either side.