Originally Posted by

**gbenguse78** I have a slight problem. Please comment on the question and solution.

A car of mass 2 Tonnes arrives at a foot of a hill, travelling at a speed of 10m/s and reaches the top of the hill with a speed of 5m/s. The hill is 500m long and rises 1 in 125. If there is a retarding force of 100N, calculate the amount of work done by the engine in getting the car up the hill.

Solution 1: Energy conservation.

I surmised the following:

Initial KE - Work done= PE gained + Final KE (Is this correct?)

Initial KE= 0.5 X 2000 X 100 = 100KJ

Work done=?

PE Gained= 2000 x 10 x 1/125 = 160J

Final KE = .5 X 2000 X 25 = 25KJ

Work Done = (100-160-25)KJ= -85KJ