- #1
rafael_josem
- 10
- 0
Hi, I need help with the following problem...
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...
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...