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Homework Help: Energy related problem

  1. Jan 11, 2009 #1
    1. The problem statement, all variables and given/known data
    Yhou built a water slide . A rider on a small sled, of total mass 80.0 kg, pushed off to start at the top of the slide (point A) with a speed of 3.0 m/s. The chute was 10 m high at the top, 55 m long, and 0.50 m wide. Along its length, 725 wheels made friction negligible. Upon leaving the chute horizontally at its bottom end (point B), the rider skimmed across the water of Long Island Sound for as much as 50 m, “skipping along like a flat pebble,” before at last coming to rest and swimming ashore, pulling his sled after him.
    (c) Find the magnitude of the force the water exerts on the sled.
    (d) Find the magnitude of the force the chute exerts on the sled at point C just before leaving the slide.

    2. Relevant equations
    PE = mgh
    KE = 1/2mv2

    3. The attempt at a solution
    PE = KE
    mgh = 1/2mv2
    I don't know were to go from here.
  2. jcsd
  3. Jan 12, 2009 #2
    You've done well so far, but are missing one component in terms of energy.

    Remember, the rider's initial velocity is given as 3.0 m/s (in the direction of the slide). Your "initial energy" equation will need both the potential energy (mgh) plus the kinetic energy from the initial velocity.

    When the rider reaches the bottom, all potential energy should become kinetic energy, as you noted.

    Now, once you have the total kinetic energy, what can you find using your equation KE = (1/2) m v2? (Hint - you know m)

    At this point, you are looking for a force that will bring the rider to a stop in 50 meters. This means there must be some force acting on the rider to make him go from his initial velocity to his final velocity (zero).

    Good luck.
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