# Homework Help: Quick Kinetic Energy question - only confirmation of answer needed.

1. Oct 17, 2009

### Griffy11

Hi guys,

Calculate the change in kinetic energy of a car of mass 2000kg if it changes its velocity from 30km/h to 60km/h

KE=1/2mv^2

So, to find the change in KE, subtract its KE when it was going 30km/h from when it was going 60km/h.

At 30km/h:
KE=1/2mv^2
KE=1/2*200*8.33^2
KE=69389J

At 60km/h:
KE=1/2mv^2
KE=1/2*2000*16.7^2
KE=278890J

So change in KE is 209501-69389
= 209501J

Is that correct, or am I doing it totally wrong?

Also - "explain the source of the energy gain" - would that just be an increase in velocity?

2. Oct 17, 2009

### rock.freak667

Yes that is correct. The source would be what is producing motion in the car in the first place. So this would be the?

3. Oct 17, 2009

### Griffy11

The driving force/friction between the tires and the road?

4. Oct 17, 2009

### rock.freak667

Well I'd just say it is the engine.

5. Oct 17, 2009

### Griffy11

Alright great, thanks for your help! :)