1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Child's Play-How high was the swing?

  1. Dec 20, 2013 #1
    1. The problem statement, all variables and given/known data
    A swing is on a rope that is 3.0 m long. The swing is 1.1 meters above the ground at its lowest point. Find its height above the ground when the rope makes an angle of 34 degrees with the vertical.

    2. Relevant equations

    3. The attempt at a solution

    Height=1.84 m

    This seems slightly off, but mostly right. Does anyone have any critiques?

    Thanks in advance!
  2. jcsd
  3. Dec 20, 2013 #2
    Try to draw the swing in it's lowest position and the 34 degree, this way you can easily find opposite, adjacent and hypotenuse.
    and why didn't use Cos(34). If you draw it, you can see it makes more sense to use cosine here.
  4. Dec 20, 2013 #3
    Ah, okay. Believe it or not, I have a diagram. xD I just couldn't decide which was which because it doesn't have a right angle.

    Trying cosine:

    cos(34)*3.0/1.1=2.26 m.

    How's that?

    Thank you!
  5. Dec 20, 2013 #4
    :) It's alright. Try drawing a straight line from the 34 degree position, perpendicular to the line marking the lowest position. Now you should have a triangle, with the 34 degree angle on top, a right angle in bottom left.
    Let me know how it goes.
  6. Dec 28, 2013 #5
    I'm sorry! For whatever reason I didn't get a notification that you posted here. I think I figured it out. I turned it in and didn't do as well as I hoped, but I finally realized why I was unsure of what was adjacent and what was opposite.
  7. Dec 28, 2013 #6
    Nope, I actually just realized I didn't figure it out yet. I was thinking of something else. Bummer.
  8. Dec 28, 2013 #7
    This would make the side with 3.0 m the hypotenuse. That doesn't look right, is that just because I am trying to trust the diagram?
  9. Dec 28, 2013 #8
    Aw! I was wondering what happened to you.
    yes the 3.0 m hypotenuse is right.
    Now, lets move back a little bit, the problem states that the rope is 3.0 m long and it's 1.1 meters above the ground at its lowest point. If we imagine it's hanging from the ceiling then we can say that the distance between the ground and ceiling is 4.1 m. right? In your diagram, mark that 4.1 m (just to visualise it).
    Now using the diagram ( 3.0 m hypotenuse and cos34) what you get is the distance from the ceiling.
    So it should be now pretty easy to find the height from the ground.
    I'll be online for now. :)
  10. Dec 28, 2013 #9
    Thanks! Sorry, but the visualizing is making it a bit harder for me. To find the height above the ground(the answer) do I use 4.1cos(34) ?
  11. Dec 28, 2013 #10
    P.S. Just a quick reminder about adjacent and opposite. The side that together with hypotenuse is making the angle you are studying, is Adjacent. And the opposite is just like it's name, it's opposite that angle.
  12. Dec 28, 2013 #11
    Yes, I finally got that part last week, AFTER turning in a paper where I was going off the hypotenuse instead of my angle. XD So was I wrong about using cos?
  13. Dec 28, 2013 #12
    No, Take a look at this diagram, you are going to find x and then subtract it from 4.1 to find your final answer.
    P.s. notice that the x is in the triangle you made, and Cos34 = adjacent / hypotenuse
    and here the x is adjacent and hypotenuse is 3 m.

    Attached Files:

  14. Dec 28, 2013 #13
    So I was right about using cosine, but I also need to remember to subtract it from 4.1? I wasn't sure if you said "No, you aren right", or "No, you are wrong."
  15. Dec 28, 2013 #14
    Sorry, The "no" was the previous post.
    You should use 3cos34, not 4.1cos34 (its should be always hypotenuse) which is 3m here.
    and as you can see in the diagram this way you calculate x which is the distance from ceiling. but you want you find the distance from ground. and we know that the distance between ceiling and ground is 4.1.
    so the final answer is: 4.1-x
  16. Dec 28, 2013 #15
    Ah, okay. Thanks! So about 1.61 meters?
  17. Dec 28, 2013 #16
    Yes! Correct :)
  18. Dec 28, 2013 #17
    That's the final answer? :-)

    You should hang around. Smiley faces and politeness, not used to that here. XD
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted