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Can somebody help me with this energy problem

  1. Apr 13, 2008 #1
    The spring in the figure has a spring constant of 1100 N/m. It is compressed 16.0 cm, then launches a 200g block. The horizontal surface is frictionless, but the block's coefficient of kinetic friction on the incline is 0.180. What distance D does the block sail through the air?

    heres a picture that should help.
     

    Attached Files:

  2. jcsd
  3. Apr 13, 2008 #2

    Doc Al

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    Well? Show your work and indicate where you got stuck.

    Hint: Use a combination of energy methods and projectile motion kinematics.
     
  4. Apr 13, 2008 #3
    Well, I first tried to use work and kinetic friction to find the horizontal distance of the hill however once I reached to the end of my calculations I figured that what I was doing found the the entire distance that the block travels. So then I tried using the conservation of energy to find the velocity of the block at the top of the hill but I don't know how to incorporate the coefficient of friction into that equation.
     
  5. Apr 13, 2008 #4
    I figure that If i can find the velocity of the block at the top of the hill then the rest of the problem is cake with kinematics
     
  6. Apr 13, 2008 #5

    Doc Al

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    Figure out the force of friction and then the work the friction does on the block as the block slides up the incline.
     
  7. Apr 13, 2008 #6
    Would the distance I use for W=Fd in this equation be the horizontal or vertical distance. Because if its the vertical distance then i can solve for v but if its the horizontal then i have 2 variables in my equation.
     
  8. Apr 13, 2008 #7

    Doc Al

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    What direction does the block move?
    You're given the angle of the incline.
     
  9. Apr 13, 2008 #8
    Ok, I found the velocity of the block at the top of the incline. Which kinematic equation and in which direction should i start?
     
  10. Apr 13, 2008 #9

    Doc Al

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    From the moment the block shoots off the incline, it's a projectile motion problem. You have the initial speed and direction.
     
  11. Mar 8, 2009 #10
    I have the same problem on my physics homework, the only difference is that the spring constant is 1300, the spring is compressed 14cm and the coefficient kinetic friction is .22.

    I found the velocity to be 11.225 m/s

    I know W=FD = (F*uk)D = mgcos45*uk*h/cos45 =mgh*uk = .8624

    I tried to read over the help given already but I really don't understand what to do, is there any further help anyone can give me??
     
  12. Mar 8, 2009 #11

    Doc Al

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    Now find the block's speed at the top of the ramp, as it shoots into the air. Then use that to determine the horizontal distance it flies before hitting the ground.
     
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