Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Forces Confusing.

  1. Nov 1, 2006 #1
    I'm confused on this problem, I have found the acceleration of the forces, but I'm stuck with the the question below. Thanks for your help!

    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 250 N. Chris's true weight is 320 N and the chair weights 160 N.

    How do you find the force Chris exerts on the chair?

    I found the accelerationg of the forces, .408m/s^2

    First of all, I know that his weight(320N) is being pushed down onto the chair. The chair also pushes him back up with (20 N, .408m/s^2 acceleration) Do I need to count in gravity also??

    The answer is 83.3 N approx and I know a combination of numbers that would allow me to get that answer:

    340N / .408 m/s^2 x 10m/s^2

    I guess that isn't right? because the result would be in mass?? Help please.
  2. jcsd
  3. Nov 1, 2006 #2
    Where is the spring scale? What is it measuring?
  4. Nov 1, 2006 #3
    It is measuring 250 N
  5. Nov 1, 2006 #4
    Right. But is he supposed to pull himself and the chair up to the apple, or is he simply pulling on a rope that is measuring the magnitude of the force he applies?

    I'm failing to see how he's going to get the apple, short of throwing the chair at it (which, oddly enough, would take less force than pulling the two of them up to it).
  6. Nov 1, 2006 #5
    well the rope is attachd to the chair and he is sitting on the chair
  7. Nov 1, 2006 #6
    and yes therefore he would be pulling the chair with himself up to the apple
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook