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!

Calculating the work against gravity?

  1. Sep 14, 2009 #1
    Calculate the work against gravity require to build the structure out of brick. Assume the brick has a density of 80 lb/ft^3.

    A tower has a height of 20ft and a square base of side 10ft.

    This is what I tired to do. I may have gotten it right, but the units or something may have been off. I am hoping one of you will be able to help me.

    Volume of layer = 10 x 10 Δy ft^3 = 100Δy ft^3
    Mass of layer = 80 lb/ft^3 x 100Δy ft^3
    Force on layer = 9.8 x 80 x 100Δy = 78400

    Taking the integral of 78400y from limits 0 to 20 equals 15,680,000, but the answer in my solutions manual says the answer should be 1.6x10^6 ft-lb.

    Can anyone help me out?
     
  2. jcsd
  3. Sep 14, 2009 #2

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    What is the acceleration of gravity in ft/s2?
     
  4. Sep 14, 2009 #3
    I'm not sure. Those were the only givens.
     
  5. Sep 14, 2009 #4

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    I guess you are supposed to know that g = 32 ft/s2. Use that.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Calculating the work against gravity?
Loading...