# Obtaining kinetic energy equation.

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1. Apr 2, 2015

### Pietervv

The question is about 2 sticks standing above eachother, but i have a more general question.

The position of my mass is described by: (2rsin(a) - rsin(b) , 2rcos(a)+rcos(b))

the goal is to get a formula for the kinetic energy, so i need the speed of the mass.

If i take the derivatives of both functions i get the speed in x and y direction.

So my question is: is it allowed for the v in (mv^2)/2 to summ up the velocities in both directions and to use it as the formula of v in the kinetic energy equation

This is my first post on this forum, so sorry for the lay-out of this question which is probably wrong...

Last edited by a moderator: May 17, 2015
2. Apr 2, 2015

### sk1105

Welcome to PF!

You can't just sum them, you have to use Pythagoras' theorem.

3. Apr 2, 2015

### haruspex

From which it follows that what you can do is calculate the KEs in the two directions separately and add those.

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