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Homework Help: Momentum qs-please help

  1. Mar 24, 2010 #1
    1. The problem statement, all variables and given/known data
    A miser sits alone in the middle of a frozen pond holding a bag of gold coins. He is unable to walk on the slippery ice. Explain how he could use the gold to rescue himself.

    2. Relevant equations

    Ft=change in p

    3. The attempt at a solution
    -i'm really not sure,but maybe he could push the gold forward and then bring it back towards himself so it collides with him. Then he will be pushed back and can move.
  2. jcsd
  3. Mar 25, 2010 #2
    Note that you have an isolated system. (Of course, you have gravitational force, but it's balanced with the reaction force of the ground.) There's no friction or any other forces.

    That means that the momentum is conserved. So, if he just throws the gold in any direction parallel to the ground (ice), it will set him in motion. Net momentum is zero in the beginning, but after he throws the gold, gold will have its momentum and, since the net momentum must be zero again (law of conservation), miser must also move (in opposite direction of the gold).
  4. Mar 25, 2010 #3
    thanks for your help, any chance you can help me with this qs (i need help on c) & d)

    Divers at Acapulco, Mexico, regularly dive head first from a heigh of 36m into water 3.6m deep. [assuming g=9.8m/s^2) and that air resistance is negligible.]
    a) What would be the vertical momentum of a 50kg diver when he reached the water?
    b)If he lost his vertial velocity by the time he reached a depth of 3.0, what average force must the water exert on him?
    c)Comment on the likely results if the inital force as he entered the water was ten times the averag force.
    d)The rocks at the base of the cliff jut more than 6m out into the water. If a diver hit these would he be killed. Why?
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