physics
posted by JIll .
You are driving a car 35mi/h down the road. The stoplight in front of you suddenly turns red and you slam on the brakes, skidding to a halt. You get out of the car and measure the skid marks made by your tires to be 28.5m meters. (Assume positive x to be in the forward direction).
A:What is the velocity of the car in meters per second?
B:What is the acceleration of the car?
C:If your car were going twice the velocity, how far would it take to stop if the acceleration were the same as for part (B)?
D:How long would it take the car to stop if it were going at twice the velocity?

a. convert mi/h to m/s: A nice thing to remember is that 60miles/hr =88feet/sec=26.8 m/s
b. Vf^2=vi^2+2ad solve for a.
c. You can work it out, using the same a. However, think: if you are going twice as fast, you have twice squared (4) times as much KE, so fricion distance must be four times as far.
d. average velocity is twice, distance is four times,
distance=velavb*time
time=distance/velocityavy=4/2= twice as long. 
18.04