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Homework Help: Tangential and normal

  1. Jan 3, 2006 #1
    an outdoor track is 65m.A runner increases her speed at a constant rate from 4 to 7 m/s over a distance of 30m.Determine the total acceleration of the runner 2s after she begins to increase her speed.

    the answer is 0.680m/s^2
  2. jcsd
  3. Jan 3, 2006 #2


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    Could you show us some of your thoughts. What is the relationship between velocity and acceleration?
  4. Jan 4, 2006 #3
    the relation is dv/dt=a.But how can i form eqn??
  5. Jan 4, 2006 #4


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    You have the linear speeds and the distance travelled while accelerating, use the equations of motion to calculate the linear acceleration - remember this is a consant acceleration.
  6. Jan 4, 2006 #5
    may i know what's the eqn of motion that u mean??
  7. Jan 4, 2006 #6
    [tex]a = \frac{v^2 - v_0^2}{2d}[/tex]
  8. Jan 4, 2006 #7
    is it possible to use acce normal + acce tangential formula??
  9. Jan 4, 2006 #8


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    The formula given by cscott is for the tangential acceleration of the girl going round the track. That is a constant value.
    Now you have to find the radial accelerartion, which is not constant. Do you know why ?
    Ans: Because ar = v²/r and v is constantly changing (in white)
    You have to find the peripheral velocity, or speed, at t = 2 sec. From that find the radial accln. Then use pythagoras' theorem with the tangential and radial accln to get the total accln.
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