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Motion - Problem

  1. Nov 14, 2009 #1
    A cyclist, Anna is travelling at a constant speed of 12m/s when she passes a stationary bus. The bus starts moving just as Anna passes, and it accelerates uniformaly at 1.5m/s.

    How long does the bus take to catch Anna??
     
  2. jcsd
  3. Nov 14, 2009 #2

    rl.bhat

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    Write down the relevant equations. Show your attempts.
     
  4. Nov 14, 2009 #3
    alright this is what i did but i didnt get the correct answer.

    equation formed
    12t=0.5*8*12 + 1.5t(t-8)

    simplify it down and i got 1.5t^2-12t-48=0, t>0 is 10.9

    answer is suppose to be 16
     
  5. Nov 14, 2009 #4

    rl.bhat

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    Bus starts from rest. So in time t the distance moved by the bus is 1/2*a*t^2. During that time distance moved by the cyclist is v*t. If the meet after this time, these distances must be equal.
     
  6. Nov 14, 2009 #5
    is a the acceleration? and why is it t^2???

    if you can, can you show me your full working out
     
  7. Nov 14, 2009 #6

    rl.bhat

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    Yes. a is the acceleration. What is the kinematic equation which contains initial velocity, acceleration, time and displacement? And unit of acceleration is m/s^2
     
  8. Nov 14, 2009 #7
    ohhhhhhhhhhhhhhh....thnx i get it now. Im suppose to use x=ut+1/at^2 formula
     
  9. Nov 14, 2009 #8

    rl.bhat

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