Hi, I need help with the following problem....(adsbygoogle = window.adsbygoogle || []).push({});

The speed limit of a school zone is 40km/h. A Driver driving at this speed sees a child that crosses the street 13m in front of the car. He applies the brakes and desacelerates at 8m/s^2. If the reaction time of the driver is 0.50s, will the car stop before it hits the child?

I did this:

40km/h : 11.11m/s

X = v^2 - V0^2/2a

X = 0 - 11.11^2/-16

X = 7.7m <== He drives 7.7m before the car stops.

Now I look for the time that the car will last to stop.

X = (v + v0/2)t

7.7 = (0+11.11/2)t

t = 1.4s

Now I add 0.5s + 1.4s = 1.9s

X = (v+v0/2)t

X = (v + 11.11/2)1.9

X = 10.5 M

According to the book, it's wrong...

Thanks...

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# Homework Help: Car deceleration physics problem

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