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Homework Help: Chris the inventive

  1. Mar 1, 2010 #1
    An inventive child named Chris wants to reach
    an apple in a tree without climbing the tree.
    Sitting in a chair connected to a rope that
    passes over a frictionless pulley, Chris pulls
    on the loose end of the rope with such a force
    that the spring scale reads 272.5 N. Chris’s
    true weight is 464 N, and the chair weighs
    67 N.
    The acceleration of gravity is g = 9.8 m/s2 .
    A. Find the magnitude of the acceleration of
    the system.
    Answer in units of m/s2.

    Find the magnitude of the force Chris exerts
    on the chair.
    Answer in units of N.

    i got the acelleration and it was marked correct (0.258380414312617702)

    but when i look for the force which i used f=ma.... it was marked wrong... i tried first in N than in kg and still nothing...
  2. jcsd
  3. Mar 1, 2010 #2


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    Homework Helper

    Chair is going up with an acceleration a. Weight of Chris acts in down ward direction. So net reaction on the chair is F = m(a+g)
  4. Mar 1, 2010 #3
    ok would i use the mass of the chair only or include the kids too?
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