# Homework Help: Help with this physics problem

1. Sep 6, 2005

### Janzen

Hey just starting physics and i am lost. This is the problem:
A car traveling 35 mi/h is to stop on a 35 meter long shoulder of the road. What minimum deceleration is required?

If you could type out How you would this is would be GREATLY appreciated.

Thanks

2. Sep 6, 2005

### NewScientist

okay well 1st of all convert mi/h to km/h because the stopping area is given in metres.

The question essentially asks how rapidly must the car decelerate in order to reach a velocity of 0 over 35 metres.

Well the average speed the car will have is 1/2 its initial velocity if we take decleration to be uniform. Therefore, using 1 mi = 1.5 k, the car will have an average speed of 26.25 km/h.

This is equivalent to 437.5m/minute or 7.29166m/second.

Therefore the car will cover the 35 metres in <5seconds.

Therefore the car must decelerate at >7m/s to stop in time

3. Sep 6, 2005

### Atomos

You might also find this formula to be very useful
$$v_2^2 = v_1^2 + 2ad$$