Easy physics problem?

1. Feb 19, 2009

jabbie3

"Easy" physics problem?

1. The problem statement, all variables and given/known data

A truck of mass 9120 kg is traveling along a level road at an initial speed of 28.8 m/s and then slows to a final speed of 13.8 m/s. Find the total work done on the truck.

2. Relevant equations

W=1/2*mv2

3. The attempt at a solution

W=1/2*(9120)*(13.8-28.2)2

this was wrong...

2. Feb 19, 2009

Delphi51

Re: "Easy" physics problem?

I agree that kinetic energy is the right approach.
Find the KE initially. Find the KE after it slows down. Take the difference. Note that the truck loses energy, so it must be doing work on the road or negative work is done on it.

3. Feb 19, 2009

Nabeshin

Re: "Easy" physics problem?

Work is not the kinetic energy, but rather the change in kinetic energy.

4. Feb 20, 2009

cjl

Re: "Easy" physics problem?

Rather than trying to combine the initial and final velocities into a difference of velocities, calculate the initial kinetic energy in its entirety, and do the same for the final kinetic energy. Once you have those, find the difference.