Physics problem need help

[MJackson09]

Hey all, here is a problem that I have for homework and I can't figure it out. Any help will be appreciated.

 

a 1650kg car accelerates from 15.9m/s to 28.1m/s in 8.31s.

a.) what is the work done on the car?

b.)what is the average power umed during acceleration?

c.)what is the average force accelerating the car?

 

So I know I have to use...

 

Work = change in kinetic energy = 1/2 (m)v^2.

 

Then what?

 

Thanks ahead of time!

[gonelli]

"change in kinetic energy" doesn't equal 1/2 (m)(v)^2

"kinetic energy" = 1/2 (m)(v)^2

 

Newton's equation (sum of)F = ma

 

And the fact that "power" means "energy per unit of time" may also be useful

[DJBruce]

Remember what change in kinetic energy actually means:

[math]w=\Delta KE=(KE_{f}-KE_{i})=(\frac{1}{2}mv_{f}^{2})-(\frac{1}{2}mv_{i}^{2})[/math]

 

Power is the rate of doing work so:

[math]P=\frac{w}{t}[/math]

 

To find force simply use Newtons second law:

 

[math]F=ma[/math]

 

You know m but you need to find a so simply use the definition of acceleration:

[math]a=\frac{\Delta v}{\Delta t}= \frac{(v_{f}-v_{i})}{\Delta t} [/math]

 

or if you want to do the first problem another way do it another way:

 

[math]W=F\cdot d[/math]

 

You know force and to find the distance simply remember your kinematic equations.

Edited August 4, 2009 by DJBruce
missed a parentheses