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: Swinging on a rope problem

  1. Oct 13, 2013 #1
    1. The problem statement, all variables and given/known data
    A hiker plans to swing on a rope across a ravine in the mountains, as illustrated in the figure, where L = 4.0 m and x = 1.8 m, and to drop when she is just above the far edge. At what minimum horizontal speed should she be moving when she starts to swing(in m/s)?


    2. Relevant equations

    Ei= Ef
    Ke = Pe

    3. The attempt at a solution

    I have the equation set up correctly but I just don't know how to find h so I can find V


    The Rope makes a isosceles triangle shape so I thought of L as adjacent, and X as the Opposite so I could solve for theta by doing Θ = arctan(1.8/4.0) = 24.22º. However, upon looking at the answer online- it says to take the arcsin(1.8/4.0) = 26.7º. Why is this?
    Last edited: Oct 13, 2013
  2. jcsd
  3. Oct 13, 2013 #2


    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    ##L## is not the side adjacent in the right triangle.

    Attached Files:

  4. Oct 14, 2013 #3

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    For that matter, x is not the base of an isosceles triangle, as TSny's diagram illustrates.
    That is not the formula for finding the apex angle of an isosceles triangle anyway.
    As TSny says: ##x\neq L\tan\theta## either.

    I'm kinda puzzled that they want you to find the angle at all.
    Since you know L and x, why not find h by pythagoras?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted