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Acceleration when time is not given

  1. Oct 25, 2010 #1
    1. A cyclist travelling 21km/hr stops over a distance of 15m. His total mass is 73kg. What is his acceleration?

    2. T=D/V, A=V/t

    3. Since time is displacement over velocity, I can use the displacement and velocity to find time and then solve acceleration by a=v/t. Am I on the right track or should the mass have come into play there?
  2. jcsd
  3. Oct 25, 2010 #2
    [tex]V_f^2=V_i^2+2ax[/tex] would work?
  4. Oct 25, 2010 #3


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    x = vt

    ...is only valid when v is constant, which it is not.
  5. Oct 25, 2010 #4
    I tried [tex] V_f^2=V_i^2+2ax [/tex] which comes to
    0=441+2a (225),

    but the answer is -1.1, error?
  6. Oct 25, 2010 #5
    I'm not sure what units you're using? Convert everything to SI units (velocity in m/s, distance in m) and it turns out fine.
  7. Oct 25, 2010 #6
    vi=21km/hr vf=0km/hr distance=15m, so do i need to convert the 21km/hr to m/s?
  8. Oct 25, 2010 #7
    nevermind I tried it again and found the right answer, thanks!
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