# Homework Help: How to solve this problem (Freefall Motion)?

1. Aug 31, 2011

### hazel31

When the front a 5.0 m long bus travelling at a constant speed of 20 m/s is 55 m away from an intersection, the traffic light turns orange. It will take 3.0 s before the light turns red. The driver's reaction time is 0.25 s. The bus can accelerate up to 2.0 m/s/s or slows down at a maximum rate of 4.3m/s/s. The intersection is 22.0 m wide. Should the driver step on the brakes or on the gas pedal? (Young, 2000)

-- I'm confused there are too many given :(

2. Aug 31, 2011

### Hootenanny

Staff Emeritus
Welcome to Physics Forums.
There are two scenarios to consider here: (a)The driver sees the amber light and decides to try and get through the intersection before the light turns red, or (b) Tries to stop before the light turns red.

So the important questions are: If the driver tries to get through the lights, will he make it? If the driver decides to try to stop, will he stop before the lights.

3. Aug 31, 2011

### hazel31

Thank You for your effort to give me a hint .. I'm sorry im just new to this forum .. Sorry Again :(

4. Aug 31, 2011

### I like Serena

Welcome to PF, hazel31!

Let's break this problem down into smaller pieces.

I'm starting with the smallest piece I can think of.
Suppose the bus driver steps on his brake immediately.
What will be his braking distance?

You will need his initial speed. What is it?
And you need the deceleration rate. What is it?
You also need a formula to calculate the corresponding braking distance.
Do you know what that formula is?