A car is travelling at 20 m/s along a road. A child runs out into the road 50m ahead and the cardriver steps on the break pedal. WHAT MUST THE CAR'S DECELERATION BE IF THE CAR IS TO STOP JUST BEFORE IT REACHES THE CHILD??????????????????????????

Initial velocity of the car, u=20 m/s

Final velocity of the car, v=0 m/s

Distance cover by the car, s=50 m

Let the constant decelaration due to the breaks be 'a',

By using equation,

v²-u²=2 a s

0 - 400 = 2 x a x 50

-400 = 100 a

a = -4 m/s

The acceleration of the car is -4 m/s.