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Homework Help: Projectile motion/forces

  1. Oct 5, 2007 #1
    1. The problem statement, all variables and given/known data
    One side of the roof of a building slopes up at 30.0°. A student throws a Frisbee onto the roof. It strikes with a speed of 15.0 m/s and does not bounce, but slides straight up the incline. The coefficient of kinetic friction between the plastic and the roof is 0.460. The Frisbee slides 10.0 m up the roof to its peak, where it goes into free-fall, following a parabolic trajectory with negligible air resistance.

    2. Relevant equations
    Determine the maximum height the Frisbee reaches above the point where it struck the roof.

    3. The attempt at a solution
    honestly... i haven't been able to do much, I try to find the acceleration using F=ma, and then maybe finding the speed when it's at the top, and continue from there; but the problem doesn't have a mass, so i don't have a clue where to start in any type of formula except for the basic kinematic equations, but i'm not even sure how those can be applied.

    I've created a free-body diagram of it, but as I said without any mass, and maybe even with it I don't know where to start ( this problem is unlike any other one we've had this chapter.) I assume that when it reaches 10m, it will have Vxf, and then I can use that as Vx0 for a new diagram for parabolic motion... but I don't know how to find A, since the only formulas for A involving force is Fk=Uk/N, and you cant get the normal force without M, because N = mass*Gravity, or since it's on a slant, n=mass*cos(30)
    Last edited: Oct 5, 2007
  2. jcsd
  3. Oct 5, 2007 #2


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    Homework Helper

    Welcome to PF!

    You are definitely on the right track. It's a 2 part problem where the answer the first part is the initial condition to the 2nd part. Just write the F = ma for the object sliding up the incline. You'll see that it is solveable.
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