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Homework Help: 1D Motion Question

  1. Aug 8, 2012 #1
    1. The problem statement, all variables and given/known data
    Give example of a motion where x>0, v<0, a>0 at a particular instant.

    2. Relevant equations
    I thought I had to give an example such as a car, ball etc.
    But the answer says:
    x(t) ie; position for time t; given by
    x(t)=A+Be[itex]^{-\gamma t}[/itex]
    where A>B, [itex]\gamma[/itex]>0 are chosen +ve constants.

    3. The attempt at a solution
    I don't know how to do it. Please help.
  2. jcsd
  3. Aug 8, 2012 #2
    the given example wasnt the only solution

    another example would be
    x(t) = 3t^2 -20t+100 at t=2

    for your example use calculus, for at t=1, x>0 as u can check
    differentiate dx/dt = -γBe^(-γt), which is less than zero at t=1
    differentiating again gives a=(γ^2)(B)(e^-yt) which is positive at t=1
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