Question

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?

Answer 1

Figure out it's change in kinetic energy.

Answer 2

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

Answer 3

Power is just going to be energy / time

Answer 4

kinetic energy is 1/2 mass * velocity^2

Answer 5

You probably want to convert units to m/s

Answer 6

Multiply by 1000 and divide by 3600?

Answer 7

Yes

Answer 8

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

Answer 9

so subtract that out and calculate the power again.

Answer 10

@applesjgtl got it?

Answer 11

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

Answer 12

@wio, still there?

Answer 13

For part a) use energy

Answer 14

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

Answer 15

Here's what I have

Answer 16

Oh, I get it. Thanks for your help!