Posted by **miyako** on Tuesday, December 21, 2010 at 1:19am.

A car that weighs 15,000 N is initially moving at 60 km/hr when the brakes are applied. The car is brought to a stop in 30 m. Assuming the force applied by the brakes is constant, determine the magnitude of the braking force.

- physics -
**drwls**, Tuesday, December 21, 2010 at 1:24am
Force x (stopping distance)

= (initial kinetic energy)

= (1/2) M V^2

For the kinetic energy, you will have to convert the weight (N) to mass (kg) and the 60 km/hr initial velocity to m/s. I assume you know how to do this.

Your answer, MV^2/(2X) will be in Newtons.

- physics -
**miyako**, Tuesday, December 21, 2010 at 2:35am
Thanks you for your quick reply. I really appreciated it, although I still cannot find the way to get the answer which is 7,086.7 N.

- physics -
**Damon**, Tuesday, December 21, 2010 at 3:44am
m = 15,000/9.8 = 1530 kg

v = 60,000 m/3600 s = 16.7 m/s

(1/2) m v^2 = 212,500 Joules

F (30) = 212,500

F = 7083 N

- physics -
**bobpursley**, Tuesday, December 21, 2010 at 3:48am
Make certain you convert the weight 15000N to mass.

Force= .5 M V^2/distance=

= .5 (Weight/g)V^2 /distance3=

= .5(15,000/9.8)*16.66^2 /30

and that gives the right answer.

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