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Homework Help: Help Me Please

  1. Nov 12, 2007 #1
    Help Me Please!!

    You don't have to actually do this, but does anyone know how to so I can solve it myself?

    1) A 50 Newton horizontal force is needed to keep an object weighing 500 Newtons moving at a constant velocity of 2.0 m/s across a horizontal surface. What is the magnitude of the frictional force acting on the object?

    2) A 40 kg mass is moving across a horizontal surface at 5 m/s. What is the magnitude of the net force required to bring the mass to a stop in 8 seconds?

    PLEASE HELP!!! Thanks!
  2. jcsd
  3. Nov 12, 2007 #2
    1) draw a free body diagram. and the frictional force is equal to the coeffecient of friction times the Normal force.

    2) draw free body diagram, us the equation of motion as well as newtons 2nd law.
  4. Nov 12, 2007 #3
    How do you find coefficient of friction and what is the equation of motion?
  5. Nov 12, 2007 #4
    coefficient of friction is usually a given in a problem, is is an intrinsic property that relates the interaction between two surfaces rubbing up against each other. F=ma is the equation of motion, knowing this and that the change in position (∆x) is equal to the change in time (∆t) times the given velocity. where the ∆x is final position minus the initial position, will help in solving the problem. I made an error in my previous post about the definition "Equation of motion" so ignore it.
  6. Nov 12, 2007 #5
    1) Divide out to find how many Newtons it takes to move at 2.0 m/s and then solve. (Assuming the answer for the coefficient of friction is to be given in N m/s)

    2) So, the object has a net inertia of 200 kg m/s and you need to stop it in 8 seconds. Is the net force any different if you need to stop it in 2hrs? or 1 second? I don't think so, but I suspect the question actually asks what is the net force in kg m/s. This is a case of units matter. Please clarify.
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