# Homework Help: Motion problem for constant acceleration of truck

1. Sep 20, 2010

### chroncile

1. The problem statement, all variables and given/known data
A truck travels at a constant speed of 28.0 m/s in the fast lane of a two-lane highway. It approaches a stationary car stopped a the side of the road. When the truck is still 125 m behind the car, the car pulls out into the slow lane with an acceleration of 2.6 m/s2. How long will it take the truck to reach the car? (Answer is 6.32 s)

2. Relevant equations
dt = dc + 125
dc = 1.3t2

3. The attempt at a solution

1.3t2 - 28.0t + 125 =

t = 15.2 s or t = 6.32 s

How do you know which answer is the correct one?

2. Sep 20, 2010

### chroncile

3. Sep 21, 2010

### zgozvrm

How did you come up with your equation? You must have started from the basic kinematic equations, right?

Go back to those and try both values of t to see which one works/makes more sense.

4. Sep 21, 2010

### zgozvrm

At the end of t=6.32s, how fast is each vehicle moving (what are their velocities)?
What is the distance covered by each in this time interval?

5. Sep 21, 2010