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Homework Help: Carousel physics. Calculating constant speed and distance.

  1. Nov 4, 2011 #1
    1. The problem statement, all variables and given/known data
    A child a rides a carousel at t = 0 and moves in a circle that is 8 m in circumference at a speed of constant modulus of 1m / s. determine:
    a) the movement of t = 0s to t = 1s
    b) the average speed from t = 0s to t = 3s
    c) the average acceleration between 1s and 3s

    2. Relevant equations
    I've got these that i figure work:
    v= vxi + vyj
    movement = Δxi + Δyj

    3. The attempt at a solution
    Given that the correct answers(provided by my textbook) should be
    a) (0,900i -0,372j)m
    b) (0,300i - 0,724j)m/s
    c) (-0,707i) m/s2

    I dont seem to know how to apply the equations above to land these answers... Vectors confuse me. For instance, Δx and Δy represent what ? I'm stuck. HELP!
  2. jcsd
  3. Nov 4, 2011 #2

    Andrew Mason

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    a) is a vector subtraction problem. Draw the displacement from the centre at t=0 and the displacement at t=1 sec. What is the difference? (ie the displacement at t=0 minus the displacement at t=1)?

    b) Use the method in a) to find the change in displacement from t=0 to t=3 sec. How would you define the average speed in terms of this displacement and the time difference?

    c) What is the change in velocity between t=1 sec. and t=3 sec? (Hint: Draw the velocity vectors at each point and subtract the velocity at t=3 from that at t=1). How would you define the average acceleration in terms of this change in velocity and the time difference?

  4. Nov 7, 2011 #3
    So ive got the a and the b down but as for c, i dont know what you mean
  5. Nov 7, 2011 #4

    Andrew Mason

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    How do you define the average acceleration?

    Hint: It involves a change in the velocity (a vector). How would you determine the change in velocity between t=1 and t=3?

  6. Nov 7, 2011 #5
    Oh wow. I put down the wrong number over and over again. But I got it. ITs -0,707i.
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