1. Not finding help here? Sign up for a free 30min 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!

Velocity and Car Acceleration

  1. Sep 19, 2007 #1
    1. The problem statement, all variables and given/known data

    A car is stopped at a traffic light. It then travels along a straight road so that its distance from the light is given by x(t)= bt^2 - ct^3, where b = 2.90 m/s^2 and c = 0.150 m/s^3.

    How long after starting from rest is the car again at rest?
    2. Relevant equations
    Already found

    Calculate the average velocity of the car for the time interval t = 0 to t = 10.0 s which is 14 m/s.

    Calculate the instantaneous velocity of the car at t=0 which is 0.

    Calculate the instantaneous velocity of the car at t=5.00 s which is v = 17.8 m/s.

    Calculate the instantaneous velocity of the car at t=10.0 s which is v = 13.0 m/s.

    3. The attempt at a solution

    I tried to find the acceleration from v = 17.8 m/s to 13.0 m/s which I got -0.96 but I don't know what equation I need to use to find the time for the car to come to a stop. I don't even know if I am on the right track.
     
  2. jcsd
  3. Sep 19, 2007 #2

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    You are given that the car begins at rest and ends at rest. So v(t)=0 at both those times. v(t)=x(t)'. If you set the equation for v(t)=0 you will find exactly two times when the car is at rest. What are they? I think you are doing fine on the other part of the problem.
     
    Last edited: Sep 19, 2007
  4. Sep 19, 2007 #3
    Ok so I got the equation 2bt - 3ct^2

    I plugged in the given values and worked it out.

    I got two values for t which are : 0, 12.8888889

    I am assuming the 12.9 is the answer.

    Am I correct Sir?

    Also, thank you very much for the help!
     
  5. Sep 19, 2007 #4

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    That's the same thing I got. Don't mention it.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Velocity and Car Acceleration
Loading...