CK-12-Physics - Intermediate

12.1. Pressure in Fluids http://www.ck12.org

FIGURE 12.2

United States quarter seen on edge.

sg=

density of material

density of water

=

8 .90 g/cm^3

1 .00 g/cm^3

= 8. 90

Check Your Understanding

1a. The nickel of the quarter in Example 1 is 0.4723 g and occupies a volume of 0.0530 cm^3. What is the density of
nickel?

Answer:

ρcopper=

m

V

=

0 .4723 g

0 .0530 cm^3

= 8 .91 g/cm^3

The densities of copper and nickel are almost the same (see Example 1). Does this surprise you? By comparison,
the density of silver is 10.5 g/cm^3 , and the density of gold is 19.3 g/cm^3.

1b. The current value of copper is 0.8455 cents per gram, and the current value of nickel is 1.8931 cents per gram.
What is the value of a United States 25-cent piece based on its metallic content?

Answer: Total value of copper=

(

0. 8455 centsg

)

( 5. 198 g) = 4. 394 cents

Total value of nickel=

(

1. 8931 centsg

)

( 0. 4723 g) = 0. 89411 → 0. 8941 cents

Total value= 4. 394 cents+ 0. 8941 cents= 5. 288 cents.

This is not too surprising when you consider that it takes the same amount of paper to print a one-dollar bill as it
does a 100 dollar bill!

2. The specific gravity of steel is 7.8. What is the density of steel in grams per cubic centimeter?

Answer: 7.8 g/cm^3. Do you see why this is so? Try the link below!

http://phet.colorado.edu/en/simulation/density

Illustrative Example 2

Let’s consider the crate inFigure12.3. The crate has a weight of 1500 N and it is initially placed on the ground.
The area of the crate that rests upon the ground is 0.750 m^2. The pressure on the crate (and the ground under the

crate) isP=FA= 01 ., 750500 mN 2 = 2 , (^000) mN 2.
If the crate is now turned on its narrow side,Figure12.4, the area which rests upon the ground is 0.40 m^2 and the
pressure isP=FA= 01 ., 400500 mN 2 = 3 , (^750) mN 2