# Fluids Physics Question

1. Apr 17, 2010

### Leo34005

1. The problem statement, all variables and given/known data
A physics book has a height of 26.0 cm, a width of 22.4 cm, and a thickness of 3.10 cm.

(a) What is the density of the physics book if it weighs 18 N?
??? kg/m3
(b) Find the pressure that the physics book exerts on a desktop when the book lies face up.
??? Pa
(c) Find the pressure that the physics book exerts on the surface of a desktop when the book is balanced on its spine.
??? Pa

2. Relevant equations

Divide the weight by gravity to get the mass.
18N/9.81 = 1.83 kg.
P = F/A

3. The attempt at a solution

Convert cm to meters:
(26.0cm)/100 = 0.26
22.4/100 = 0.224
3.10/100 = 0.031
Now divide
1.83/(0.26*0.224*0.031) = 1.83/0.00180544 = 1014 kg/m^3
P = F/A
area of the book = (0.224*0.26) = 0.5824 m^2
18/0.5824 = 30.9 Pa

When balanced on its spine, its width and thickness make up the area
(0.224*0.0310) = 0.006944
18/0.006944 = 2592 Pa

2. Apr 17, 2010

### AtticusFinch

You got the first two right, but I would say that you should use height in the last problem instead of width.

3. Apr 18, 2010

### Leo34005

Like i said, I believe my answer is wrong. If someone would double check it.

4. Apr 18, 2010

### AtticusFinch

That's what I'm saying. Your answer is wrong because you used the wrong number in your calculations. All you need to do is use the right one.