# Minimum Stopping Distance

1. Jan 13, 2008

### ae4jm

[SOLVED] Minimum Stopping Distance

1. The problem statement, all variables and given/known data
The minimum stopping distance for a car traveling at a speed of 30m/s is 60m, including the distance traveled during the driver's reaction time of 0.50s.

a.What is the minimum stopping distance for the same car traveling at a speed of 40 m/s?

b. Draw a position-versus-time graph for the motion of the car in part a. Assume the car is at Xo=0m when the driver first sees the emergency situation ahead that calls for a rapid halt.

2. Relevant equations
For a part:
Vf=Vi+at

d=((Vi+Vf)/2)*t

3. The attempt at a solution

The correct answer for a part is 100m. I'm getting 96.7m. I started with the given and figured the time to be 5.335s, using Vf=Vi+at, and subtracted .5s for the reaction time. Then I used d=((Vi+Vf)/2)*t, which I got 96.7m. I don't think that I'm plugging into the formulas correctly?

2. Jan 13, 2008

### Kurdt

Staff Emeritus
The car will not stop in the same time. But its acceleration is constant. Try $v^2 = u^2 +2as$

3. Jan 13, 2008

### ae4jm

Okay, I got the acceleration from the given information and then used the equation you have given to solve for a. part. Thanks for the help--it is greatly appreaciated.