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Homework Help: Newton's laws problems HELP !

  1. Jan 16, 2008 #1
    newton's laws problems HELP!!!!!!!!!!!!!!!!

    These are the problems that I either tried and thought I got the wrong answer :eek: or got half-way through and got completely stuck on. :bugeye: Any help would be greatly appreciated.:redface: Thanks!!! :wink:

    1. A 43.8-kg sign is suspended by two ropes with angles of 43 and 55. Find the tension in each rope.

    2. A 75-kg crate is resting on a table. The coefficient of static friction between the crate and the table top is 0.68. What is the maximum mass m of the hanging box for which the system will remain at rest?

    3. An electric motor is lowering a 452-kg crate with an acceleration of 1.60m/s^2. Determine the tension in the cable.

    4. A 205-kg log is pulled up a ramp by means of a rope that is parallel to the surface of the ramp. The ramp is inclined at 30 degrees with respect to the horizontal. The coefficient of kinetic friction between the log and the ramp is 0.900, and the log has an acceleration of 0.800m/s^2. Find the tension in the rope.

    5. An elevator in a tall building is allowed to reach a maximum speed of 3.5m/s going down. What must the tension be in the cable to stop this elevator over a distance of 3.0m if the 3elevator has a mass of 1300kg including occupants?

    6. A fisherman in a boat is using a "10-lb test" fishing line. This means that the line can exert a force of 45N without breaking (1lb=4.45N).
    a) How heavy a fish can the fisherman land if he pulls the fish up vertically at a constant speed?
    b) If he accelerates the fish upwards at 2.0m/s^2, what maximum weight fish can he land?

    7. A block (mass m1) lying on a frictionless inclined plane is connected to a mass m2 by a massless cord passing over a pulley.
    a) Determine a formula for the acceleration of the system in terms of m1, m2, theta, and g (gravity).
    b) What conditions apply to masses m1 and m2 for the acceleration to be in one direction (say, m1 down the plane), or in the opposite direction?

    8. Suppose the coefficient of kinetic friction between m1 and the plane (related to problem 7) is 0.15, and that m1=m2=2.7kg. As m2 moves down, determine the magnitude and direction of the acceleration of m1 and m2, given theta = 25 degrees.

    9. What smallest value of the coefficient of kinetic friction will keep the system of problem 8 from accelerating?

    Explanations or instructions will be helpful instead of just answers. :biggrin: I don't want to just know what the answer is. :yuck: I need to understand how to do the problem otherwise I will never pass physics. :confused: I'm here to learn.:smile: Please and thank you's!!!!!! :approve:

    P.S. ALTHOUGH...if you don't want to go through the trouble of explaining, the answers will at least enable me to check mine, so if that's all you're willing to do, that would help, too. THANKS!
    Last edited: Jan 16, 2008
  2. jcsd
  3. Jan 16, 2008 #2


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    Homework Helper

    Show us your work/answers first. You must show your work in order to get help.
  4. Jan 17, 2008 #3
    It's too hard to show the work, and, as I said, some of the problems I was completely stuck on. Anyway, it's too late now. I don't need it anymore. I do understand where you're coming from, though. Thanks anyway.
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