# Density of Moon Rock: Solve Mass with Pressure

• needhelp83
In summary, the geologist is trying to find the density of a moon rock that has a mass of 7.85 kg and an apparent mass of 6.18 kg when submerged in water. They use the concept of buoyancy to solve this problem, where the upward force is equivalent to the weight of the displaced water. By using the density of water (1kg/liter), they calculate the difference in weight between the rock in air and in water, and use this to find the density of the rock to be 4700.6 kg/m3. The density of air is negligible in this problem.
needhelp83
A geologist finds that a moon rock whose mass is 7.85 kg has an apparent mass of 6.18 kg when submerged in water. What is the density of the rock

Would I use pressure to solve for the mass of the moon rock?

When submerged in water, the object displaces an equivalent volume of water. That displaced water weighs something, and it not being there provides some effective bouyancy. Like, if you have a baloon under water, the upward force is equivalent to the weight of the missing water. Does that help you solve this problem?

Wouldn't I need the volume of water it was placed into?

Not if you're dealing with densities...

p=m/V

1000 kg/m^3=7.85 kg/V
1000V=7.85
V=0.00785 m^3

p=m/V
p=7.85 kg/0.00785 m^3
p= 1000 density of rock

Did I get off somewhere?

Do I now need to use the density of air?

The mass density of the air is negligible in this problem, and you need to use the mass density of water to give you the lift component force that lightens the moon rock when it is under water. Remember that the density of water is 1kg/liter. So the difference between the 7.85kg weight and the 6.18kg weight is the weight of the displaced water...

This should be better...

pwaterVg=FB
(1000 kg/m3)(9.8 m/s)V=(7.85 kg – 6.18 kg)(9.8 m/s)\
V=0.00167 m3

p=m/V
p = 7.85 kg/0.00167 m3= 4700.6 kg/m3

Am I on the right track now?

## 1. What is the density of moon rock?

The density of moon rock varies depending on the specific type of rock, but on average it is around 3.3 grams per cubic centimeter.

## 2. How is the density of moon rock calculated?

The density of moon rock is calculated by dividing its mass by its volume. In order to accurately calculate the density, the mass needs to be measured in grams and the volume in cubic centimeters.

## 3. What is the relationship between mass and pressure in regards to density?

The relationship between mass and pressure in regards to density is that as the pressure on a substance increases, its volume decreases, resulting in an increase in density. This is known as the direct relationship between density and pressure.

## 4. How does the density of moon rock compare to other types of rock?

The density of moon rock is generally lower than that of Earth rock, with the exception of some types of basalt found on the moon. This is due to the moon's lower gravity and lack of erosion processes that can compact and increase the density of rocks on Earth.

## 5. Why is it important to know the density of moon rock?

Knowing the density of moon rock is important for understanding the composition and structure of the moon's surface. It can also provide insights into the moon's formation and evolution, as well as potential resources that could be extracted in future lunar missions.

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