physics
posted by miyako .
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.

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. 
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.

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 
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.