Solution

By considering the slope as the inclined plane and let the acceleration of the car on that slope is a

Let force acting on the car to moves - down

= mg sin –  mg cos

= mg [sin – cos]

acceleration of the car

  = 10 × 0.25 = 2.5m/s2

Given, initial velocity of the car u =21.6km/hr = 6m/s

Given, length of the slope = 12.8m

from v2 – u2 = 2as,

v2 = u2 + 2as = (6)2 + 2 × 2.5 × 12.8

   = 36 + 64 = 100m

v  = 10m/s (or) = 36km/hr.

Therefore how hard the driver applies the brakes, the car will reach the bottom with a speed greater than 36km/hr.

This is the minimum speed with which the car reaches the bottom.