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The problem statement, all variables and given/known data

1). Suppose a car is traveling at 12.0 m/s, and the driver sees a traffic light turn red. After 0.510s have elapsed (the reaction time), the driver applies the brakes, and the car decelerates at 6.20 m/s^2. What is the stopping distance of the car, as measured from the point where the driver first notices the red light?

2). A cement block accidentally falls from rest from the ledge of a 53.0m high building. When the block is 14.0m above the ground, a 2.00m tall man looks up and notices that the block is directly above him. How much time, at most, does the man have to get out of the way?

Relevant equations

1). I tried to use the equation: x = v0t + 1/2 at^2.

2). see below

The attempt at a solution

1). I tried saying that a = -6.20 m/s^2, the initial velocity v0 = 12, and that time = 0.510s, but I didn't get the right answer (17.7m).

2). a = -9.80 while initial velocity v0 = 0. However, I'm not sure exactly how I should go around calculating displacement. After I find displacement though, should I use the equation x = v0t + 1/2 at^2 to find the time?

Any pointers would be greatly appreciated!

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# Homework Help: Physics Kinematics problems

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