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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?
    m/s2
    (b) If it starts from rest, how far will it move in 10 s?
    m
    (c) What will its velocity be at the end of this time interval?
    m/s
     
  2. jcsd
  3. Oct 3, 2005 #2

    hotvette

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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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