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Homework Help: Hey I really NEed help ( for my finals)

  1. Jan 22, 2008 #1
    hey i have finals tomoro and i have to make a poster out of this problem ..
    but i can even do this problem ..i v tried it tho.

    A police officer is sitting at the side of the road on a motorbike with the engine running, monitoring motorist's speeds with a speed gun. The speedlimit is 100 km/h. A motorist passes the police officer at 120 km/h and as the car passes, the police officer starts from rest and chases the motorist with uniform accelaration of 3 m/s^2.
    A) How long does it take for the police officer to reach the car?
    B) What is the maximum speed of the police offficer?
    C) What is the distance travvled by the two vehilcles, when the police officer reaches the car.
    D) What distance does it take for the car to come to a stop?
    E) Skatch a velocity time graph of the motion of the two vehicles on the same set of axes.

    i have the answers but i dont know how he got them ? i need to show my work .:(

    a 200/9 s
    b 200/3 m/s
    c 20000/27 m
    d depends how you want to do deceleration
    e time on x velocity on y, car is flat line at y=120
    bike is parabola y=3x^2

    please help out thx
  2. jcsd
  3. Jan 23, 2008 #2
  4. Jan 23, 2008 #3


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    Science Advisor
    Homework Helper

    There are three equation sof motion
    v = u + at
    v^2 = u^2 + 2as
    s = ut + 1/2 at^2
    Where v=final velocity, u=initial velocity, s=distance t=time a=accelration.

    Most of these questions consist of picking which equations you have most of the values for, writing the equation for both objects then setting the equations equal to each other.
    Be careful to use the same units and in questions about rising and falling objects be careful about the sign of accelration.
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