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Homework Help: Stuck on a Conservation of Energy problem!

  1. Nov 26, 2009 #1
    1. The problem statement, all variables and given/known data
    A 1.9-kg block slides down a curved, frictionless ramp. The top of the ramp is 1.5m above the ground; the bottom of the ramp is 0.25m above the ground. The block leaves the ramp moving horizontally, and lands distance D away.

    A) What is distance D away?

    B) Suppose the ramp is not frictionless. Find the distance D for the case in which friction on the ramp does 9.7 J of work on the block before it enters the horizontal (and still frictionless) section towards D.

    For both A) and B) the time is 4.0s at distance D.

    2. Relevant equations
    Potential Energy (1) + Kinetic Energy (1) = Potential Energy (2) + Kinetic Energy (2)
    mgh(1) + 1/2*m*v^2(1) = mgh(2) + 1/2*m*v^2(2)

    (basically the first part is at the top of the ramp and the final is at the bottom of the ramp)

    3. The attempt at a solution
    Since the ramp is frictionless, the block is going at a constant speed. However, when I tried using the equation it didn't work out so there's probably another way.
  2. jcsd
  3. Nov 26, 2009 #2


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    Science Advisor
    Homework Helper

    You have posted the correct formula. However, the block is accelerated: it has no velocity at the top, but a positive velocity at the bottom. Obviously, m and g are given in the problem. Can you give me the appropriate values for h(1), v(1), h(2) and v(2) ?
  4. Nov 26, 2009 #3
    h(1) is 1.5m (reference point is the ground).

    h(2) is 0.25m (reference point is the ground).

    We don't know v(1) or v(2).
  5. Nov 26, 2009 #4

    Doc Al

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    Staff: Mentor

    I would presume that the block starts from rest at the top of the ramp. So v(1) = 0. Use energy conservation to solve for v(2).
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