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Linear and Angular Motion Help

  1. Oct 26, 2014 #1
    1. The problem statement, all variables and given/known data
    Need a bit off help with these questions would appreciate some help.

    2. Relevant equations
    1. An accelerating vehicle crosses a datum with a velocity of 20m/s and then covers a distance of 2.5km in 50s. Calculate the acceleration, and the velocity reached after it has travelled 2.5km.

    2. If a rotor is rotating at 2000 rev/min accelerates to 3000 rev/min in 6 seconds calculate its acceleration and angle turned through.

    3. Calculate the velocity of a belt in a belt drive system where the pulley is 82.3cm diameter and rotates at:
    a) 1750 rev/min
    b) 40 rev/s

    3. The attempt at a solution
    1. a=v-u / t
    20/50 = 0.4m/s^2

    v=u+at
    20 + 0.4 x 50 = 40m/s

    2. 314.16 - 209.43 / 6 = 17.5 rad/s^2

    w= wo t + 1/2 a t^2
    1256.58 + 315
    = 1571.58 rad

    3. Unsure how to do this one

    Thanks
     
  2. jcsd
  3. Oct 26, 2014 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    This assumes the velocity changes by 20m/s in 50 seconds. You don't know if that is true.
    Simple cross-check: if the vehicle drives with a speed between 20m/s and 40m/s, in 50s it cannot go further than 40m/s*50s = 2km. Certainly not 2.5km.
    Checks like those are useful to see if your answer can make sense.
    There are missing brackets, but this problem will vanish with proper fractions on paper.
    I can confirm your answer.

    3. The pulley is a circle, the belt is moving at the outer edge with the same speed as this outer edge.
     
  4. Oct 26, 2014 #3
    Unsure what you mean with Q1. Am i using wrong formulas?

    had a go at 3.

    a)V=Rw
    0.41x183.26
    =75.14m/s

    b)V=Rw
    0.41x251.33
    =103.04m/s
     
  5. Oct 26, 2014 #4

    mfb

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    2016 Award

    Staff: Mentor

    Yes.

    3 looks good.

    As a general remark, it is easier to understand what you are doing if you start with a formula, and with the values given in the problem statement.
     
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