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Homework Help: Sliding block

  1. Jun 10, 2007 #1
    I am stuck on this 3 part problem and dont really know what to dooo, any help would be greatly appreciated =)

    A block (mass 569 grams) starts at rest and slides down a frictionless track except for a small rough area on a horizontal section of the track. It leaves the track horizontally, flies through the air, and subsequently strikes the ground 4.61 m away. THe acceleration of gravity is 9.81 m/s^2. A) At what height h above the ground is the block released? B) What is the speed of the block when it leaves the track? C) What is the total speed of the block when it hits the ground?

    The vertical distance between the horizontal section of the track and the ground is 1.9m. The height from where the block is released is uknown. And at the horizontal of the track there is a 1 m horizontal section where friction exists, and the coefficient of friction there is .3.

    help please! thanksss =)
  2. jcsd
  3. Jun 10, 2007 #2
    Start by: Finding the speed as the block leaves the horizontal ramp. Use kinematics to find how long it would take an object to accelerate 1.9 m, distance from the track to the ground, then use that time and the distance 4.61 m to find the block's speed as it leaves the ramp. Hope that helps a lil.
  4. Jun 10, 2007 #3
    Alright i did that, i found the speed as it leaves the track and i got : 7.407 m/s.

    So to find the height.... because KE = PE.... then (mv^2)/2 = mgh --> h=(v^2)/2g and i got 2.7963 for my height...? is that correct?

    Thats as far as I am getting, other than that i dont know how to do part c...

    help again pleaaase
  5. Jun 10, 2007 #4
    for part c, i found the total energy (KE + PE) and i got 26.2143. THen i did 26.2143 = (1/2)mv^2 and solved for v and got 9.599 m/s^2. Is that my velocity as it hits the ground? Dont i have to account for the friction?
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