Question

A car traveling at 20 minutes/seconds when the driver sees a child standing in the road. He takes 0.80 seconds to react, 10 steps on the brakes and slows at 7.0 m/s Square. How far does the car go before it stops?

Answer 1

I assume you mean 20 m/s.

In the first 0.80 seconds, the car travels:

20*0.80 = 16 m

During the period of deceleration, you can calculate the distance travelled using:


`v^(2) = u^(2) + 2as` where s is the distance travelled, v is the final speed (0), u is the initial speed (20 m/s), and a is the acceleration (-7.0 m/s^2).

This gives:

2*7.0s = 20^2
14.0s = 400
s = 400/14 m

The total distance the car travels is:

16 + 400/14 = 44.6 m (3 s.f.)