Homework Help: physics repost

Posted by Anonymous on Wednesday, April 16, 2008 at 8:46pm.

A car of mass 1330 kg is traveling at 28.0 m/s. The driver applies the brakes to bring the car to rest over a distance of 79.0 m. Calculate the retarding force acting on the car.

same as before just posting again so you wont have to scroll. heres my work

KE=1/2*m*v^2
KE=521360

KE=Ff*d
521360*Ff*79.0
521360/79.0
6599.5=Ff
I have to convert that to N, so
6599.5*9.80
= 64675 N what did I do wrong this time?

physics repost - Damon, Wednesday, April 16, 2008 at 8:51pm
6599.5=Ff
That IS in Newtons

The 9.8 is acceleration of gravity, used to calculate the weight in Newtons of something on earth surface given the mass in kilograms. It is not needed here. There is no weight involved here, only mass and change of momentum.
physics repost - Anonymous, Wednesday, April 16, 2008 at 8:53pm
thank you. great explaination

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