Question

A DRIVER TAKES 0.20S TO APPLY THE BRAKES AFTER HE SEES A NEED FOR IT. THIS IS CALLED THE REACTION TIME OF THE DRIVER . IF HE IS DRIVING A CAR AT A SPEED OF 54 KM/H AND THE BRAKES CAUSE A DECELERATION OF 6.0M/S2, FIND THE DISTANCE TRAVELLED BY THE CAR AFTER HE SEES THE NEED TO PUT THE BRAKES ON.

Answer 1

time taken by the case to stop after brakes are applied

t = v/a

here,

v = velocity = 54km/h = 15m/s

a = acceleration = 6m/s

so,

t = 15/6 = 2.5s

now,

total time taken after the driver sees the need to apply the brakes will be

T = 2.5s + 0.2s = 2.7s

now,

the total distance travelled in this time will be

s = uT + (1/2)aT²

or

s = 15x2.7 + (1/2)x6x2.7²

thus, we get

s = 62.37 m