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Homework Help: Few problems

  1. Jun 20, 2005 #1
    a ball with the mass of 50 grams hangs on a very light thread who has the lenght of 80 cm and swing back and forth (pendel). At the begining of the movement the maximum angle that the thread formed when moving was 35 degress, but after one minute tha angle had declined to 2o degress.The time for the ball to make one swing from its lowest point to its highest remained the same.

    The question is: Is the power that the swinging energi (mekanic energi) from the pendel turns into other energi forms under one minute bigger or smaller than the averge power of the pendel?


    A boy has build himself a treehouse that is located 3.8 meters above the groud. He has also build a device that consists of a small platform he can stand on. The platform is attached to a rope that runs throw a
    small easily moveable wheel located above the threehouse. With this device the boy can be pulled up to the threehouse by somebody pulling the rope from the ground. The boys mass it 39 kg (boy a), two other boys that help pulling him up have the mass of 34 kg (boy b) and 32 kg (boy c).

    Halfway pulling the platform up to the threehouse with boy A standing on it, suddenly boy c lets the rope go, while boy b hang on to it.

    the questions are:
    a) With what violocity will boy A hit the ground?
    b) How high above the ground will boy B go?
    A mousetrap is used as a engine for a small car with the mass of 50 gram.The car mus be able to travel 8 meters. the mousetraps arm is about 4 cm, and it can be pulled 180 degress. The force needed to pull the arm of the mousetrap is linear dependable to the turning angle. its at its lowest point 2 N and on its highest about 10 newton.

    the question is: What it the maximum violocity this car can have?
  2. jcsd
  3. Jun 20, 2005 #2
    You can calculate the answer to this problem by considering free body diagrams around each of the two boys and resolving forces, if you assume a frictionless pully and an inelastic rope - both boys will accelerate at the same rate. All you need is F=ma. I started the calculations but need to go, sorry I can't be more help.