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October 22, 2014

Homework Help: Physics

Posted by Matoro on Sunday, December 9, 2012 at 3:45pm.

The (nonconservative) force propelling a 1.50E3 kg car up a mountain road does 4.70E6 j of work on the car. The car starts from rest at sea level and has a speed of 27.0 m/s at an altitude of 2.00E2 m above sea level. Obtain the work done on the car by the combined forces of friction and air resitstance, both of which are nonconservative forces.

This is Chapter 6, Work and Energy, of Physics, 8th Edition, by Cutnell, #55.

I know it has something to do with initial and final energies being equal.

I also know that kinetic and gravitational potential are the only two energies involved.

I got this from Answers:


Total Energy (at end) = KE + PE

So set this equal to Wdone - Wdiss

Wdiss = Wdone - KE - PE
Wdone = 4.7e6 J
KE = (1/2)mv^2
PE = mgh
m = 1.5e3 kg
v = 27 m/s
h = 2e2 m

Wdiss = 4.7e6 - .5 * 1.5e3 * 27^2 - 1.5e3 * 9.8 * 2e2

But I'm not totally sure what all the symbols mean and how the answer was reached. Any help is appreciated!

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