411 REFERENCE · Wikibooks
The Physics Problem Solver/Mechanics/Work and Energy
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A car of mass 1 Mg is parked on a level road with its handbrake on.
Another car of mass 1.5 Mg travelling at 10 m · s−1 collides with the back of the stationary car.
The two cars move together after collision in the same straight line.
They travel 25 m before finally coming to rest.
Find the average frictional force exerted on the cars as they come to rest.