i cannot work this out can you help please?

a) Its initial kinetic energy was: ½mv². This is reduced to zero when the car stops; so the loss of KE is ½mv². Convert the velocity from "km/h" to "meters/sec", and this will make the KE number come out in Joules (the standard unit).

b) change in KE = total work done = force × distance

You in Part (a) that the change in KE is ½mv², and you know that the distance is 125 meters. Substitute:

½mv² = force × 125 meters

or:

force = ½mv² / (125 meters)

Note that this is the force that the ROAD exerted on the wheels of the car. They asked for "the force required at the brakes," which seems to mean the force of your foot on the brake. This is almost certainly NOT the same as the amount of force exerted by the road, and there's no way to determine it without more info. Tell that to your teacher.

a) kinetic energy is (1/2)mv^2 when it's moving, and 0 when it is stopped.

b) The work done by the brakes is W = F * d. The work is the same as the loss in kinetic energy, so you have W. And you have d.

V = 90/3.6 = 25 m/s

a = V²/(2x) = 2.5 m/sec²

a) KE = ½m*V² = 437500 J

b) F = m*a = 3500 N