# Homework Help: Deceleration problem!

1. Sep 9, 2007

### ballerinajen426

1. The problem statement, all variables and given/known data

The driver of a pick up truck going 100 km/h applies the brakes, giving the truck a uniform deceleration of 6.5m/s(squared) while it travels 20.0 m
a) what is the speed of the truck in km/h at the end of tihs distance
b) how much time has elapsed

her is the thing i have the answers but no way of showing my work and with the change in units km/h m/s i get mixed up PLEASE HELP!

a) 81.4 km/h
b) 0.794 s

2. Sep 9, 2007

### bob1182006

Ok so what would you do first for a)?

what formula would you use to solve for the final speed of the truck?

also I think you need to do b) before you can do a).

so what equation can you use to solve for the time elapsed?

When you're going to change the units just make sure to show your work really good in order to spot an error.

Other than that I don't think I can help you out more without giving the answer away.
Just show some work even if you do it wrong at least we'll see if you are going on the right track and just messed up on units/etc...

3. Sep 9, 2007

### EvanQ

a)
try the formula u^2 = v^2 + 2as
where u=initial velocity, v=final velocity, a=acceleration (will be a negative), and s=the distance traveled.

b)
try using v = u + at
using the final velocity that you found in section a.
t will give you time.