Calculating the work against gravity?

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Homework Help Overview

The discussion revolves around calculating the work done against gravity to construct a brick tower. The problem involves determining the work required based on the tower's dimensions and the density of the bricks used.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to calculate the work by integrating the force on each layer of the tower, but expresses uncertainty about the units and the final result. Some participants question the value of gravitational acceleration to be used in the calculations.

Discussion Status

Participants are exploring different aspects of the problem, including the correct value for gravitational acceleration. There is a mix of interpretations regarding the calculations and the assumptions made about the given values.

Contextual Notes

There is a noted discrepancy between the original poster's calculated result and the answer provided in their solutions manual. Additionally, there is uncertainty about the appropriate value for gravitational acceleration in the context of the problem.

mscott
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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?
 
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What is the acceleration of gravity in ft/s2?
 
I'm not sure. Those were the only givens.
 
I guess you are supposed to know that g = 32 ft/s2. Use that.
 

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