# AP Physics 2 : Pressure

## Example Questions

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### Example Question #21 : Pressure

Paul weighs . What must be the surface area of his shoe if he uses it to try to kill an ant? Assume the shoe applies uniform force, he can only apply as much force as his weight, and his other foot is not in contact with the ground. The ant cannot withstand any pressure greater than

Explanation:

Pressure is force divided by area. The force Paul applies is . The rest is just algebra.

### Example Question #55 : Fluid Statics

A glass is filled with water. The gauge pressure at the top of the glass is zero and the gauge pressure at the bottom is . A second glass with half the height and twice the diameter of the first glass is also filled with water. What is the gauge pressure at the bottom of the second glass?

Explanation:

Pressure  so the diameter changing does not matter but half the height changes the pressure of the second glass to .

### Example Question #56 : Fluid Statics

Suppose that a barometer is filled with water, as shown in the diagram below. If this barometer's column has a height of , what would be the height of a barometer that used mercury instead of water?

Note: Mercury has a specific gravity of .

Explanation:

For this question, we're asked to see how the height of a barometer's column will change once the liquid changes from water to mercury.

Barometers are a measure of atmospheric pressure. As the ambient pressure pushes down on the surface of the liquid, this pressure is transmitted throughout the liquid, such that it causes the liquid level in the water to rise. As the ambient pressure increases, the column in the barometer climbs.

We'll need to use the equation for pressure as it relates to density and height.

Since the ambient pressure is the same in both instances, we can set these terms equal to each other. That is to say, it doesn't matter which liquid is being used in the column, because both of them will feel the same pressure from the atmosphere.

Next, we can rearrange the above expression to isolate the term for the height in the mercury column.

Finally, we can plug in the terms given to us in the question stem to arrive at our answer.

### Example Question #57 : Fluid Statics

Determine the pressure  below the surface of freshwater.

None of these

Explanation:

Pressure is equal to force over area:

The force will be due to the gravity of the water above. The mass of the water will be the density times the volume.

The volume will be equal to the base area times the length

Combining equations

Plugging in values:

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