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Homework Help: Velocity and Displacement Question

  1. Jan 20, 2005 #1
    I got this homework the other day and 2 of the questions I don't even know where to start. The worst thing is when I ask the teacher he says he hasn't got time to go over it and help! :mad:

    Here are the questions, thanks in advance:
    1) Your car heads north at 25ms^-1. Another car approaches along a side road, coming west at 20ms^-1. Both are 100m from where the roads join. Sketch the positions and velocities of the two cars. What is the velocity of the other car as seen from your car?
    2) Air traffic control detects an aircraft on a bearing 090 degrees (due E). Radar pulses return with a delay of 0.2 m s. 100s later it is detected on a bearing of 120 degrees, with pulse delay 0.173 m s. What is the displacement vector of the aircraft?

    Pretty long questions, I know. :tongue2: It would be cool if someone could just give me the method and not actually do the questions for me. :rofl:

  2. jcsd
  3. Jan 20, 2005 #2
    Some hints:

    1. Draw a coordinate system and affix directions to the velocity and displacement vectors in this sytem.

    2. Use the relative displacement equation, differentiate it once (or twice) to get velocity (or acceleration) as desired.

    3. Use a consistent sign convention throughout and don't affix signs to algebraic quantities that are to be determined.

  4. Jan 20, 2005 #3
    Ok, thanks for the fast reply!
    I've done the first question easily now, thanks for the help. But I still can't seem to do the second one. :(
    If someone could go through it for me I would be very grateful. :P
  5. Jan 21, 2005 #4
    If I understand your second problem correctly, pulse delay refers to the time taken for a signal to travel to the airplane and back to the ATC so in this time, the airplane too changes course/moves to a different position. Convert the degrees (bearings) into meaningful quantities using vectors.

    If you need more help post your solution here and I'll be happy to see it.

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