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Physics Puzzler!

  1. Nov 11, 2003 #1
    HELP!!!!! I am in grade 12 physics and my teacher gave us a puzzler for the weekend. I need serious help with it and all of my classmates cant figure it out either! The question is :

    A 10.8 kg box is 5.0 m from the edge of a 12.96 m high cliff. Bob pushes the box over the edge of the cliff by applying a constant horizontal force to it until the box goes over the edge. The force of friction on the box is 49.0 N and the box lands 7.5 m from the base of the cliff. How much force did Bob apply to the box while he was pushing?

    What do I do and can someone show me how to solve it?
     
  2. jcsd
  3. Nov 14, 2003 #2
    A 10.8 kg box is 5.0 m from the edge of a 12.96 m high cliff. Bob pushes the box over the edge of the cliff by applying a constant horizontal force to it until the box goes over the edge. The force of friction on the box is 49.0 N and the box lands 7.5 m from the base of the cliff. How much force did Bob apply to the box while he was pushing?

    If v is the (horiz.) velocity at push-off and t the time of fall;
    vt = 7.5; (1/2) gt^2 = 12.96; Find v.
    Total work done by all forces till push-off,
    (F-49)5 = Kinetic energy at push-off = (1/2) (10.8) v^2
     
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