Homework Help: Physics

Posted by Anonymous on Thursday, September 3, 2009 at 9:50pm.

The speed limit in a school zone is 40 km/h. A driver traveling at this speed sees a child run into the road 23 m ahead of hs car. He applies the brakes, and the car decelerates at a uniform rate of 8.0m/s^2. if the driver's reaction time is .25s, will the car stop before hitting the child?

Physics - Anonymous, Thursday, September 3, 2009 at 10:07pm
Using Vf = Vi + at we can calculate how long it will take the car to stop from 11.11 m/s. It will take 1.39s but the reaction time adds .25s so it the time it takes will be 1.64s to stop the car.
Now use S = Vit + (1/2)at^2 to see if the car will stop before 23m.

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