Question

A train is moving at a speed of 90km/h. on applying brakes, a retardation of 2.5m/s^2is created. At what distance before, should the driver apply the brakes to stop the train at the station

Answer 1

Given  u = 90 kmph 
               = 90 * 5/18 = 25 m/s
            v = 0.
           a = - 2.5 m/s²

We have the equation of motion:
    v² = u² + 2 a s 
    0 = 25² - 2 * 2.5 * s
    s = 125 meters.

So the train travels 125 meters before it comes to a halt.

Answer 2

V(final speed) = 90 km/hr = 25m/s

U(initial speed)= 0

Retardation = 2.5m/s^2

S (distance )= ?

V=U+at

25 = 0 + 2.5(t)

t= 10s

S = ut + 1/2at^2

S= (0)(10) + 1/2(2.5)(10)^2

S = 1/2 x 2.5 x 10 x 10

S = 125m