Please help me on this physics problem?

Question

A car is traveling 25 m/s when the driver sees a child standing on the road. He takes 0.8 s to react, then steps on the brakes and slows at 7.0 m/s2. How far does the car go before it stops? please help. ive been struggling with this one all day long. first accurate answer gets 10 points!!! thanks!

Answer 1

You want to find stopping distance s given:

initial speed u = 25 m/s,

final speed v =  0,

acceleration a = - 7.0 m/s^2.

Using the equation v^2 = u^2 + 2as:

0 = 25^2 + 2(- 7.0)s

= 625 - 14s

s = 625 / 14

= 44.64 m.

The total distance travelled is s plus the distance travelled before breaking starts. That is:

25 * 0.8 = 20 m.

Total stopping distance

= 44.64 + 20

= 64.6 m to 3sf.