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: Sin Rule & Pythagoras?

  1. Jan 25, 2009 #1
    1. The problem statement, all variables and given/known data
    The two sides of a stepladder are of length 2m and 1.85m. When fully opened, the longer side is inclined at 65° to the horizontal. Find the distance apart of the feet of the step ladder.

    2. Relevant equations
    Sin Rule & Pythagoras?

    3. The attempt at a solution
    I had a go but I really think it's wrong.


    [itex]\frac{2}{\sin90°} = \frac{b}{\sin65°}[/itex]

    [itex]b = \frac{2}{\sin90°}\times \sin65°[/itex]

    [itex]b = 1.81 (2d.p.)[/itex]

    [itex]a^2 = 2^2 - 1.81^2 = 0.7239[/itex]

    [itex]a = 0.85 (2d.p.)[/itex]

    [itex]x^2 = 1.85^2 - 0.85^2 = 2.7[/itex]

    [itex]x = 1.64 (2d.p.)[/itex]

    [itex]l = 1.81 + 1.64 = 3.45m[/itex]

    P.S. How do you do new lines in LaTeX?
  2. jcsd
  3. Jan 25, 2009 #2
    Re: Ladder

    How do you know that the top angle is 90 degrees when it is fully opened? I think you have to stick with just the 65 degree angle and the leg lengths in order to find the distance.

    Also, I don't know how to do new lines in LateX. I always just close the tex tag and start a new one.
  4. Jan 26, 2009 #3
    Re: Ladder

    I thought it would be 90 degrees because it says 65 degree to the horizontal.
  5. Jan 26, 2009 #4
    Re: Ladder

    You cant assume that the ladder opens up at 90 degrees (it doesnt actually).
  6. Jan 26, 2009 #5
    Re: Ladder

    I see what I did wrong. I got horizontal and verticle mixed up so I drew my diagram wrong.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook