# Find velocity given height

1. Apr 28, 2014

An apple falls from a tree and hits Sir Isaac Newton on the head. If the apple fell from 2.5m, what was the velocity of the apple just before it hit him?

This question was on my physics exam today, and no one I've talked to in my class was able to get it! Dont we need two variables at the very least?

2. Apr 28, 2014

### collinsmark

Welcome to Physics Forums!

There are two ways to solve this problem.

• You can use of your kinematics equations for uniform acceleration. Find the one that relates velocity and distance (technically, displacement), with a constant (uniform) acceleration. Or,
• You can use conservation of energy.

You'll need to know the acceleration due to gravity. Depending on your textbook coursework, this is typically 10 m/s2, 9.8 m/s2 or 9.81 m/s2 depending on how precise your textbook/coursework wants you to be. With that you should be able to solve for the final velocity.

3. Apr 28, 2014

### phinds

If the problem really says "the apple fell from 2.5m" then you need to know how high off the ground it hit him. If the problem really says "the apple fell 2.5m" then you have everything you need.