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Homework Help: Instantaneous Velocity of a electron with a provided formula (Solved)

  1. Jan 10, 2016 #1
    1. The problem statement, all variables and given/known data
    The motion of an electron is given by x(t)=pt^3 +qt^2 +r, with p = -1.9 m/s^3 , q = +1.3 m/s^2 , and r = +9.0 m.

    What is the velocity at: a) t=0s b) t=1s c) t=2s d t=3s

    2. Relevant equations
    3. The attempt at a solution
    I have tried plugging in the time to equal to t, in which for a) i got +9 b)8.4 c)-1 d)-30.6
    At this point I'm not sure what to do, and I'm totally lost...
  2. jcsd
  3. Jan 10, 2016 #2

    Ray Vickson

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    Whoever told you that v = x/t? That is almost always false! That is why Newton (or maybe Leibniz) invented calculus, and why you had to learn it.
  4. Jan 10, 2016 #3
    Would it be v=d/t?
  5. Jan 10, 2016 #4


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    Staff Emeritus
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    You're overlooking some obvious hints here.
    1. instantaneous velocity
    2. calculus
  6. Jan 10, 2016 #5
    you are probably talking about v=dx/dt
  7. Jan 10, 2016 #6
    I haven't learned how to take derivatives yet using Calculus, my Calculus course just started and we haven't covered much so far. Is there possibly another way of solving this without the use of Calculus?
  8. Jan 10, 2016 #7
    i don't think so o_O
    that is really wierd... you teachers should be more carefull.. you sure you didn't even touched derivatives while learning kinematics?
  9. Jan 10, 2016 #8
    100% we haven't yet... This and another question that is also part of my assignment asks the same thing..
  10. Jan 10, 2016 #9
    Okay, I searched up on YouTube on how to take derivatives, so I took the derivative of my equation in which it becomes x'(t)=3pt^2+2qt+0. Afterwards I plugged in the time into the t's and got my answer! Thanks WrongMan by helping me "accidentally" find what derivatives are when I tried searching up the meaning of v=dx/dt
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