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Homework Help: Need help with projectile/friction problem.

  1. Nov 3, 2007 #1
    A popular pastime is to see who can push an object closest to the edge of a table without its going off. You push the 100 g object and release it 3.00 m from the table edge. Unfortunately, you push a little too hard. The object slides across, sails off the edge, falls 1.30 m to the floor, and lands 25.0 cm from the edge of the table.

    If the coefficient of kinetic friction is 0.500, what was the object's speed as you released it?

    I've tried a lot of different things, suggestions?
  2. jcsd
  3. Nov 4, 2007 #2
    I don't know if this will help but have u tried

    kinetic energy = gravitational potential energy

    1mv^2/2 = mgh
  4. Nov 4, 2007 #3
    t = time to fall
    y = vertical distance
    g = acceleration (9.8m/s^2)
    x = distance traveled off table
    v1 = initial speed
    v2 = speed as object leaves table (x component)

    y = (1/2)*g*t^2 therefore t = (2*y/g)^(1/2)
    x = v2*t therefore x = v2*(2*y/g)^(1/2)

    Maybe someone can finish this for you. I apologize my laptop is dying:(
  5. Nov 4, 2007 #4
    try to figure out the velocity when it leaves the table and starts falling. If you find it, you can find its kinetic energy at the instant. Since there is friction on the table, the kinetic friction caused the mass to be slowed down from the initial velocity it took off from. how much did it slow down, or how much energy did it lose to friction? If you know that than, you can trace back and find the initial velocity.
    Last edited: Nov 4, 2007
  6. Nov 4, 2007 #5


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    Please keep in mind that the rules of this forum are that the "helpers" should only guide the OP, not do or work out the solution.

  7. Nov 4, 2007 #6
    Got it. Thanks ya'll. really helped.
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