## applesjgtl 2 years ago A car weighing 1400kg accelerates from 90 km/hr to 110 km/hr in 6.0s. a) assuming no friction, what was the power output of the car? b) If a frictional force of 700 N acted on the car over a distance of 400 m during the same 6.0-second acceleration, what would be the power output of the car if the same speed increase was observed?

1. wio

Figure out it's change in kinetic energy.

2. wio

You have the mass and two velocities. So calculate the kinetic energy before and after acceleration.

3. wio

Power is just going to be energy / time

4. wio

kinetic energy is 1/2 mass * velocity^2

5. wio

You probably want to convert units to m/s

6. applesjgtl

Multiply by 1000 and divide by 3600?

7. wio

Yes

8. wio

For b) " 700 N acted on the car over a distance of 400 m" Just remember that work = force * distance that will tell you how much energy was taken away

9. wio

so subtract that out and calculate the power again.

10. wio

@applesjgtl got it?

11. applesjgtl

For part a, what value do I use for energy? Is it KE2-KE1?

12. applesjgtl

@wio, still there?

13. wio

For part a) use energy

14. wio

then divide the change in energy by time to get power output.

15. applesjgtl

Here's what I have

16. applesjgtl

Oh, I get it. Thanks for your help!