- #1

AJKing

- 104

- 2

## Homework Statement

Eight bricks, each 6.0 cm thick with a mass of 1.5 kg, lie flat on a table. How much work is required to stack them one on top of another?

h

_{brick}= 0.060 m

m = 1.5 kg

## Homework Equations

W = Fd

F

_{g}= m*g

## The Attempt at a Solution

I tried the following, and was correct. Please read the fourth point for my question.

F

_{g}= 1.5*9.8 = 14.7 N

W

_{t}= W

_{1}+W

_{2}+W

_{3}+W

_{4}+W

_{5}+W

_{6}+W

_{7}+W

_{8}

W

_{t}= 14.7*0 + 14.7*.06 + . . . + 14.7*0.42 = 25 J

**4. My question**

The answer to the question goes a little something exactly like this:

8 bricks each with m = 1.5 kg

height of each brick h= 0.060m

centre of mass is lifted 3.5 h

W = (8*1.5*9.8)(3.5*0.060) = 25 J

Where did that 3.5 come from?

7 bricks lifted divided by 2? Oh . . . Probably. Yeah. Averages and what not.

Writing this helped. Might as well post it.