Average Power and speed of a car

[nagaromo]

1. A 2000kg car, initially at rest, is accelerated along a horizontal roadway at 3m/s^2. What is the average power required to bring the car to a final speed of 20m/s?



2. I don't know the relevant equations :(



3. Well I first tried force multiplied by the final velocity which is 120000 watts, but that's not the answer. Please help!

 

[gneill]

The velocity increases linearly if the acceleration is constant. What does that say about the average velocity as compared to the final velocity over the distance (or time) concerned?

 

[bacon]

nagaromo,
Take a look at this tutorial posted by Mr. Bernhardt, specifically page 99 that deals with the concept of power. Equation 5.54 is for instantaneous power, but the average power is given by the total change in energy(start to finish) divided by the total time.
Think about how the energy of the car changes(the work done) and how to figure out how long it takes for the change to occur.

The reason your first attempt was wrong is that you calculated the instantaneous power at the very end of the push, when the car was at it's final speed. You want the average, over the whole push.

 

[bacon]

Sorry, I forgot to include the reference.

https://www.physicsforums.com/attachment.php?attachmentid=13010&d=1205093282

 

[nagaromo]

oo now i got the right answer. thanks guy! i appreciate the help :D

 

[nagaromo]

60000w right? :d:d:d

 

[bacon]

That's the answer I got.

 

[nagaromo]

thanks! <3 :]