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: Vertical Deflection Off Free End Of Bar

  1. Nov 12, 2012 #1
    1. The problem statement, all variables and given/known data

    The drawing shows a 152-kg crate hanging from the end of a steel bar. The length of the bar is 0.09 m, and its cross-sectional area is 3.80x10^-4 m^2. Neglect the weight of the bar itself.

    (a) Determine the shear stress on the bar.
    (b) Determine the vertical deflection ΔY of the right end of the bar.

    2. Relevant equations

    Not quite sure what to do with deflection. I found ΔY=(F/A)(L/G) off another posts. Correct to use in this case?

    3. The attempt at a solution

    (a) This was pretty simple. Just found tension which was (152kg)(9.8). Then divided that by (3.8x10^-4). I got 3920000 N/m^2

    (b) This is where I am having trouble. I used the equation off another problem.
    This gave me ΔY=(3920000N/m^2)(.09m/(2.0x10^11)).
    I found 2.0x10^11 by looking around for Young's Modulus of steel. This gave me an answer of 1.764x10^-6. However, the answer was marked wrong.

    Help please!
  2. jcsd
  3. Nov 12, 2012 #2


    User Avatar
    Homework Helper

    I assume you have a cantilever type of beam with a point load of 152 kg acting at the free end. In which case for this type of loading, the end deflection is given by

    δ= FL3/3EI

    Look up cantilever end deflection for definition of the terms.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook