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Homework Help: Took test-wanted to check answers

  1. Sep 23, 2008 #1
    I just finished a test in my physics course and want to see if I answered correctly on a few questions.

    1. A box is being supported by two massless ropes that are 30 degrees from vertical. The box exerts a force of 410 N in the negative direction. What is the force on each rope.
    The picture he gave us showd a diagram with force and weight pointing straight down. He had two ropes pointing up from the force vector with each pointing 30 degrees from vertical(a 60 degree angle between the two). I found the answer to be 235 N on each rope.

    2. A rock is thrown straight up at a velocity of 39 m/s. How long does it take to hit the ground?
    I found it to be 8 s. I think this is right. I figured this by Vf=Vi+at. If this is correct then it would be 0-39/9.8=t=4s. I then doubled this for the return. Am I correct?

    3. What happens when you spring into the air?
    a. The earth has a force in the positive direction that is more than weight so it push you up.
    b. You push a force down greater than weight and the earth pushes back with an equal force pushing you upwards.

    4. You throw a rock upwards off of a cliff at an angle of 40 degrees. The initial velocity is 30 m/s. The total flight time is 75 s. How far away does it land?
  2. jcsd
  3. Sep 23, 2008 #2


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    So what did you put as your answers for 3 and 4?
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