# Motion at constant acceleration

## Homework Statement

In coming to a stop, a car leaves skid marks 92m long on the highway. Assuming a deceleration of 7.00m/s^2 estimate the speed of the car just before braking.

## Homework Equations

deceleration=7m/s^2, distance=92m

## The Attempt at a Solution

I found there was not enough information to solve the problem, but i had a go, assuming dividing the distance by deceleration you would get time. 92/7 =13.14 seconds

I substituted this into the equation of motion x=x0+v0t+1/2at^2
=52.99m/s. Is this right???????

NEED TO KNOW BY TOMORROW

## Answers and Replies

ideasrule
Homework Helper
Why would distance divided by deceleration give you time? Why would x=x0+v0t+1/2at^2, which is an equation for displacement, give you speed?

Are you familiar with the equation vf^2-vi^2=2ad?

so the answer should be vi^2=2(7)(92)
=square root 1288=35.889 m/s??