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: The average velocity of the point - numerical value of t

  1. Feb 7, 2015 #1
    1. The problem statement, all variables and given/known data

    During the first t seconds of motion, the average velocity of the point is zero. What is the numerical value of t?

    2. Relevant equations

    3. The attempt at a solution

    I don't understand this question. I understand that the average velocity is zero if the displacement in the denominator is zero. E.g. if a body is moving in a circle. Or if a body moves to the right and then to the left and distances cancel out. But how could you give the numerical value of t?
    I thought t tended to zero (as a limit): 0.0000000001 but it is wrong.
    Am I overlooking something obvious?
  2. jcsd
  3. Feb 7, 2015 #2


    User Avatar

    Staff: Mentor

    I think we're missing some context here. Is this part of a larger question? (The problem mentions "the point", not "a point", so it seems to be referring to something previously defined).
  4. Feb 7, 2015 #3
    Oh yes, silly me. This is an equation from the previous question. I will do it now. That's English for you. Many thanks.

  5. Feb 7, 2015 #4


    User Avatar

    Staff: Mentor

    So at time t=0, what's the initial position according to your equation?

    When is the position again that value?
  6. Feb 7, 2015 #5
    It is simple now.
    I need the displacement = 0 so

    at t = 0 initial position x(i) is -4.

    The displacement:

    I can't assume that t=0 because you can't divide by 0. (the average velocity = displacement/time elapsed)

    2*(9/4)-3*(3/2)=9/2-9/2=0 :)

    Many thanks. :) :) :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted