# At the instant when the traffic light turns green, a car starts with a constant accel

1. Oct 10, 2011

### rayj098

1. The problem statement

At the instant when the traffic light turns green, a car starts with a constant acceleration of 1.8 m/s^2 [forward]. At the same instant a truck traveling with a constant velocity of 8.5 m/s [forward] overtakes and passes the car. How far from the starting point will the car catch up to the truck?

2. The attempt at a solution
Car:
d = V1*t + 1/2*a*t^2
d= 0 + 1/2(1.8)(t)^2
d= 0.9t^2

Truck:
d = V * t
d = 25t

Put it all together

0.9t^2 = 25t
0.9t^2 - 25t = 0

Now what?

2. Oct 10, 2011

### whoareyou

Re: At the instant when the traffic light turns green, a car starts with a constant a

I think your equation for your truck is wrong. After you have the two equations, put them together and solve for time.

3. Oct 10, 2011

### rayj098

Re: At the instant when the traffic light turns green, a car starts with a constant a

How is the truck equation wrong? Please expand

4. Oct 10, 2011

### whoareyou

Re: At the instant when the traffic light turns green, a car starts with a constant a

In the question, it says that the truck is traveling at a constant velocity of 8.5m/s [F] and in your equation, you have 25 as the velocity.