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PLEASE HELP: Newtons law question

  1. Jan 28, 2008 #1
    a 20 kg box is on frictionless surface acted on by two horizontal surfaces. when in same direction, it pulls 11 m/s but in opposite directions, it pulls only 1 m/s. determine magnitude of each force.
    answer: 120 N , 100 N

    okay...i need help with this. i am using newtons law: force=mass x accelleration
    i am trying to find force. mass is 20 kg and accelleration is 11 m/s. when i plug in that number, i get 220N. can someone please help?
  2. jcsd
  3. Jan 28, 2008 #2


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    You've got a couple of typos here, as noted above. Otherwise, you have solved for the net force when the body is accelerating at 11m/s^2. 220N is the net force. It is the algebraic sum of the 2 forces. You need to look at the 1m/s^2 acceleration case to get another equation before you can solve for the individual forces.
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