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Homework Help: Need Help on Forces

  1. Oct 3, 2005 #1
    I have a worksheet I recieved for make-up since I was absent. It is really hard since I miss the lesson. All the problems are similar, but I do no know where to start. Here is a sample problem. Will someone show me steps on how to do it?

    A boat moves through the water with two forces acting on it. One is a 2.1 103 N forward push by the motor, and the other is a 1.9 103 N resistive force due to the water.
    (a) What is the acceleration of the 1200 kg boat?
    (b) If it starts from rest, how far will it move in 10 s?
    (c) What will its velocity be at the end of this time interval?
  2. jcsd
  3. Oct 3, 2005 #2


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    Homework Helper

    You need the basic equation of motion for an object:

    [tex]\Sigma F_i = m a_i[/tex]

    In other words, in each coordinate direction, the sum of forces on an object is equal to the mass of the object times acceleration (i.e. second derivative of x with respect to t). Integrate twice to get x(t), evaluate the initial conditions from the problem statement, then solve from there.
  4. Oct 3, 2005 #3
    so would it be 200 N = 1200kg X A. v I tried that and i was told i was wrong.
  5. Oct 3, 2005 #4
    2.1 x 10^3 1.9x10^3 so 2100 n 1900 s0 2100-1900= 200??
  6. Oct 3, 2005 #5

    Doc Al

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    Staff: Mentor

    I figured out what you meant. Yes: The net force is 200 N and the acceleration will be given via Newton's law, just like you wrote in post #3.
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