# Homework Help: Life in the Fast Lane

1. Nov 8, 2004

### PhysicsNovice

Hello Everyone. I am almost through my on-line coarse on Introductory Physics. I am taking my last self-assessment before the on-line certification in two weeks. There is just one problem that has my confused. Please provide some guidance. Thanks.

Accelerating Car - What is the average power required to accelerate a 1200 kg car from rest to a velocity of 20 m/s in 10 seconds?

I am not even sure exactly where to start. I know that power can be measured in joules/sec a metric unit known as a watt. I do know some related formulas that might apply. They include:

Power = Change in Energy/Change in time
F = ma
W = Fd

I am still unclear how to proceed to determine that answer to this question in watts.

2. Nov 8, 2004

### Galileo

You have another:
KE=1/2mv^2.

3. Nov 8, 2004

### PhysicsNovice

How appropriate. If anyone can help me it is the master of falling (accelerating) bodies...Galileo. Anyway, I am still confused on why your formula is the one I should start with. Can you explain? If I do use this formula I get:

KE=(1/2)(1200kg)(20m/s)^2
KE=(.5)(1200)(400)
KE=240,000

Now, is this watts? Also, is it important to consider the 10 second time in calculating the avergae power? If so then maybe the answer should be 240,000/10=24,000 watts. What do you think? I am on tract? Thanks.

4. Nov 8, 2004

### Galileo

Looks good to me

The car is started at rest, so it had no kinetic energy.
After 10 seconds it had 240,000 J of kinetic energy.

So it gained 24.000 J per second on average.