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Force Exerted?

  1. Sep 25, 2007 #1
    [SOLVED] Force Exerted???

    A child holds a sled on a frictionless snow covered hill, inclined at a 34 degree angle

    if the sled weighs 73N find the force exerted on the rope by the child. answer in units of N
    and find the force exerted on the sled by the hill, answer in units of N
     
    Last edited: Sep 25, 2007
  2. jcsd
  3. Sep 25, 2007 #2
    the force on the rope would be 73N to equal out the 73N of the sled

    and the force the hill exerts on the sled would be either 0 cuz its frictionless or 73N to equal out the 73N of the sled as well and preventing it from sinking thru the hill????
     
    Last edited: Sep 25, 2007
  4. Sep 25, 2007 #3
    this whole thing with the angle is what throws me off on this problem
     
  5. Sep 25, 2007 #4

    learningphysics

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    No, don't forget the normal force the hill exerts.

    draw a freebody diagram... what are the forces acting along the incline?
     
  6. Sep 25, 2007 #5
    woudlnt the force on the rope just be 73N to equual that of the sled tho?
     
  7. Sep 25, 2007 #6

    learningphysics

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    No. Draw the freebody diagram of the sled. There is a normal force that acts perpendicular to the incline... Gravity acts downwards... divide gravity into two components... one that acts perpendicular to the incline(opposite the direction of the normal)... one that acts parallel to the incline...

    What is the component of gravity perpendicular to the incline... what is the component of gravity parallel to the incline.
     
  8. Sep 25, 2007 #7
    do u mean draw it out liek a triangle and calculate the forces straight down and also the forces to the right?
     
  9. Sep 25, 2007 #8
    then use sin34 to find out the down force and the horizontal force

    and get down force to be 40.82 and horizontal force to be 60.519?
     
  10. Sep 25, 2007 #9
    or am i not even close to doin this the right way?
     
  11. Sep 25, 2007 #10

    learningphysics

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    You are very close... make sure you have the angles right. What is the angle between the the gravity vector downwards... and the component perpendicular to the incline?
     
  12. Sep 25, 2007 #11
    the angles are 90 degrees 34 degrees and 56 degrees???

    i cannot figure out what formulas to use to figure this out... this problem is confusing when it shouldnt be blahhh

    keep in mind i need the force exerted on the rope

    and the force exerted on the sled by the hill
     
    Last edited: Sep 25, 2007
  13. Sep 25, 2007 #12

    learningphysics

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    Yes, but which one is 34 and which one is 56? Look at the triangle formed by gravity and its two components... you need an angle in that triangle... then you can use sin and cos...
     
  14. Sep 25, 2007 #13
    the angle with gravity is 56 degrees..... but the problem says nothing about gravity so why am i takin that into accoutn?

    i need to know that for the force exerted on the rope?
     
  15. Sep 25, 2007 #14

    learningphysics

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    you can't get the tension in the rope until you know the component of gravity acting along the incline...

    Look at this page: under where it says "frames of reference":

    http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Dynamics/InclinePlanePhys.html

    see the two components of gravity?
     
  16. Sep 25, 2007 #15
    ok i see the 2 components of gravity... and am i right in saying the 3 angles in the problem are 34, 56, and 90??? those are the 3 i need to solve this??
     
  17. Sep 25, 2007 #16

    learningphysics

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    yes. 34 is what you need. it's the [tex]\theta[/tex] angle like in the link I sent. So what is the component of gravity perpendicular to the plane? What is the component of gravity parallel to the plane?
     
  18. Sep 25, 2007 #17
    so its mass*gravity sin34

    and the one perpendicular is mass *gravity cos 34????
     
  19. Sep 25, 2007 #18

    learningphysics

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    yes, so in this case... the parallel component is 73*sin34. And the perpendicular component is 73*cos34.

    so taking the sled and rope as one system... what are the two forces acting on this system parallel to the plane? This will give you the answer to the first part...

    what are the forces acting perpendicular to the plane? That gives the secod part.
     
  20. Sep 25, 2007 #19
    well the parallel component is equal to 40.821
    the perp is 60.519
    the 2 forces acting on this system are 73N and 40.821N???
     
  21. Sep 25, 2007 #20

    learningphysics

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    how are you getting these numbers?

    oops... never mind I had my calculator wrongly setup...

    ok... so the two forces parallel are 40.821 and the force the boy exerts on the rope... so what's the force the boy exerts on the rope?
     
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