1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Motion at constant acceleration

  1. Mar 14, 2010 #1
    1. The problem statement, all variables and given/known data
    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.


    2. Relevant equations

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

    3. 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
     
  2. jcsd
  3. Mar 14, 2010 #2

    ideasrule

    User Avatar
    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?
     
  4. Mar 15, 2010 #3
    so the answer should be vi^2=2(7)(92)
    =square root 1288=35.889 m/s??
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook