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!

First derivative problem

  1. Jun 4, 2014 #1
    A Car, initially travelling at the speed 100 km/h, slows down according to the formula. L(t)= At - Bt^2
    Where L is the travelled distance, t is the time & B= 90 km/h^2. Using derivative, find the time moment when the car speed becomes 10 km/h. Find the acceleration of the car at this moment.

    i think this is a function (my interpretation below)

    50(t)= 100t - 90t^2

    would i just have to graph the function?

    any guidance appreciated
     
    Last edited: Jun 4, 2014
  2. jcsd
  3. Jun 4, 2014 #2

    CAF123

    User Avatar
    Gold Member

    That formula for L(t) is reminiscent of a constant acceleration motion. So you can find the negative acceleration of the car by inspection (since you know B).

    Why is there a 50t on the LHS of your equation?

    What definitions of velocity and acceleration do you have? In particular, ones relating to position?
     
  4. Jun 4, 2014 #3
    The car has a velocity of 100km/h and slows down to 10km/h?

    The 50 was just a random distance number. Disregard it.
     
  5. Jun 4, 2014 #4

    CAF123

    User Avatar
    Gold Member

    Yes. You can think of the situation as the car applying brakes and decelerating at a constant rate.
     
  6. Jun 4, 2014 #5
    Do you know where i could do some reading to find out where to begin with this problem?
     
  7. Jun 4, 2014 #6

    CAF123

    User Avatar
    Gold Member

    Do you have an introductory physics textbook? E.g see the first few chapters of Halliday, Resnick, Walker.

    Related links:
    Section 1 and 3.1 of http://en.wikipedia.org/wiki/Acceleration

    If you want to understand things well though, nothing beats a good textbook and the accompanying problems.
     
  8. Jun 4, 2014 #7
    If you know calculus, then the first derivative of distance is velocity, and the second derivative is acceleration.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: First derivative problem
  1. Derivative Problem (Replies: 2)

  2. Derivative Problem (Replies: 1)

  3. Derivative problem (Replies: 6)

  4. Derivative problem (Replies: 2)

Loading...