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Working out speed, kinetic energy and resistive force

  1. Nov 9, 2015 #1
    1. The problem statement, all variables and given/known data
    JU261dI.png

    2. Relevant equations


    3. The attempt at a solution

    a) I'm not sure how to calculate speed without having both distance and time but I believe it will revolve around calculating gravitational potential energy and kinetic energy.

    bi) I think this is just simply using the formula kinetic energy = 1⁄2 × mass × speed2.

    bii/biii) I'm really struggling to work out these. I think It might revolve around using the speed from the first question and then take it away from 22m/s.
     
  2. jcsd
  3. Nov 9, 2015 #2

    haruspex

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    You are on the right track for a) and b.i).
    I suggest you solve those two first. It might then be more apparent how to solve b.ii)
     
  4. Nov 9, 2015 #3
    I believe I have solved them now.
    TUukwDk.png
    if possible could you help with the last one?
     
  5. Nov 9, 2015 #4

    haruspex

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    What equation do you know relating work and distance?
     
  6. Nov 9, 2015 #5
    Work = Force x Distance.?
     
  7. Nov 9, 2015 #6

    haruspex

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    Looks promising. How would it apply here? Explain in words.
     
  8. Nov 9, 2015 #7
    is it something like:
    Work done = change in kinetic energy,
    Work = - 11250 J?
     
  9. Nov 9, 2015 #8

    haruspex

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    Yes, but I meant the work = force x distance equation. Can you express that in respect of frictional force and the circumstances in this question?
     
  10. Nov 9, 2015 #9
    The amount of work done is equal to the frictional force times by the distance? I'm sorry i'm not 100% sure.
     
  11. Nov 9, 2015 #10

    haruspex

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    Yes (given that the force is constant; in general the relationship is an integral).
     
  12. Nov 9, 2015 #11
    Am I able to work out the magnitude from this?
     
  13. Nov 10, 2015 #12

    haruspex

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    Yes, you have all the information. (One clarification: the force is not constant as a vector here, but it is constant in magnitude. This works out ok because the force of friction is always parallel to the motion, so it still reduces to force x distance travelled along the path. You do not know and do not need to know the end-to-end displacement as a vector.)
     
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