# Homework Help: Kinematic Problem

1. Feb 28, 2005

### ireneooi

Hi,really need help with this question.
A motorist travelling at 13 m/s aprroaches traffic lights which turn red when he is 25m away from the stop line.His reaction time(i.e. the interval between seeing the red light and applying the brakes)is 0.7s and the condition of the road and his tyres is such that the car cannot slow down at a rate of more than 4.5 ms-2.If he brakes fully,how far from the stop line will he stop,and on which side of it?

2. Feb 28, 2005

### ramollari

Please show us some effort from u! It is not that we cannot give you help.

3. Feb 28, 2005

use the very simple kinematics equations available. Manipulate them to et an answer. If you have a more specific probem in this question, please state it. Nobody will solve your problem for you.

$$V^2 = {V_o}^2 + 2ad$$
$$d = V_o t + \frac{1}{2} at^2$$
$$V = \frac{d}{t}$$

Regards,

4. Feb 28, 2005

### ireneooi

Oh,sorry,I actually just have one problem,which is the acceleration part of the question.Can anyone just explain what it means?Thanks.

5. Feb 28, 2005

### dextercioby

It's a deceleration.With constant acceleration $a=-4.5ms^{-2}$...

Daniel.