# Homework Help?

1. Sep 9, 2004

### tumbler19

I have been working on this problem for a while, and I still don't understand how to set it up for the first part of this problem:

At the instant the traffic light turns green, an automobile starts with a constant acceleration a of 2.2 m/s squared. At the same instant a truck, traveling with a constant speed of 9.5 m/s, overtakes and passes the automobile.

(A) How far beyond the traffic signal will the automile overtake the truck?

(B) How fast will the automobile be traveling at that instant?

2. Sep 9, 2004

### Leong

Use this formula,
$$s=ut+\frac{1}{2}at^2$$
Initial velocity for the car is u=0.
Constanst acceleration for the truck is a=0.
$$s_{car}=1.1t^2$$
$$s_{truck}=9.5t$$
s is the position relative to the origin / traffic light.

Part (a)
When the automobile overtakes the truck, their positions relative to the traffic light is the same. so, we have
$$s_{car}=s_{truck}$$. find the t when this happens and substitute back either of the equation for s above because they will be at the same position relative to traffic light.

Part (b)
Use this formula,
$$v=u+at$$

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