Pressure

Help Questions

AP Physics 1 › Pressure

Questions 1 - 10
1

A sealed container holds water at rest. Point A is $0.20,\text{m}$ below the surface; point B is $0.50,\text{m}$ below the surface. Pressure is due to fluid depth. Which point has greater water pressure?

They are equal because pressure depends only on container shape

Point B, because pressure increases with depth

Point A, because it is closer to the surface

They are equal because the container is sealed

Explanation

This question assesses understanding of hydrostatic pressure in fluids, which increases with depth. In a fluid at rest, pressure at a depth h is P = ρgh + P_atm, where ρ is density, g is gravity, and h is depth, showing pressure grows linearly with depth. Point A at 0.20 m has less pressure than Point B at 0.50 m due to the greater overlying fluid weight at B. Thus, Point B experiences greater water pressure. Distractor C suggests equal pressure because the container is sealed, but sealing does not affect the depth dependence. A useful strategy is to compare depths directly, as pressure differences depend solely on Δh in the same fluid.

2

A $400,\text{N}$ crate rests on the floor on four identical square feet. Each foot has area $1.0\times10^{-3},\text{m}^2$. Pressure is due to contact force. What is the pressure on the floor under one foot?

$4.0\times10^5,\text{Pa}$

$4.0\times10^2,\text{Pa}$

$1.0\times10^5,\text{Pa}$

$1.0\times10^2,\text{Pa}$

Explanation

This question tests pressure due to contact force, defined as force per unit area. Pressure is P = F/A, where F is the perpendicular force on the surface. The 400 N crate is supported by four feet, so each foot bears 100 N, and with area 1.0 × $10^{-3}$ m², the pressure per foot is 100 / 0.001 = 1.0 × $10^5$ Pa. This calculation assumes even weight distribution across the feet. Distractor B (4.0 × $10^5$ Pa) might come from using the total force instead of per foot. When analyzing multi-support contacts, divide the total force equally among supports before applying P = F/A.

3

A lake is calm. Point C is $1.0,\text{m}$ below the surface and point D is $3.0,\text{m}$ below the surface. Pressure is due to fluid depth. How does the water pressure at D compare to at C?

Greater at D, because pressure increases with depth

Equal, because pressure depends on the lake’s shape, not depth

Equal, because both points are in the same lake

Less at D, because deeper water has less room to expand

Explanation

This question tests hydrostatic pressure, emphasizing its increase with fluid depth. Hydrostatic pressure is P = ρgh + P0, directly proportional to depth h below the surface. Point C at 1.0 m has lower pressure than Point D at 3.0 m, where the pressure is three times greater due to triple the depth. Therefore, pressure is greater at D because of the increased depth. Choice B is a distractor claiming equal pressure since both are in the same lake, ignoring depth's role. For such problems, always focus on the depth from the surface as the determining factor for pressure comparisons.

4

A crate exerts a $200,\text{N}$ normal force on the floor. Pressure is due to contact force. If its contact area doubles, what happens to the pressure?

It is cut in half because the same force is distributed over twice the area.

It stays the same because the force is unchanged.

It becomes zero because the force is spread out.

It doubles because pressure is proportional to area.

Explanation

This question tests understanding of the inverse relationship between pressure and area. Pressure is defined as P = F/A, so if force remains constant at 200 N while area doubles, pressure becomes half of its original value. Mathematically, if initial pressure is P₁ = F/A, then new pressure is P₂ = F/(2A) = (F/A)/2 = P₁/2. Choice B incorrectly suggests pressure remains constant, ignoring the role of area in the pressure equation. To solve pressure problems with changing conditions, apply P = F/A systematically and note which variables change.

5

In a column of water at rest, pressure is due to fluid depth. Point $M$ is $0.20,\text{m}$ deeper than point $N$. Which statement is correct?

$p_M>p_N$ because deeper points have more fluid above them.

The pressures depend on the container’s shape, not depth.

$p_N>p_M$ because pressure decreases as you go down.

$p_M=p_N$ because the water’s density is the same at both points.

Explanation

This question tests understanding of pressure variation with depth in fluids. In any static fluid, pressure increases with depth following P = P₀ + ρgh. Since point M is 0.20 m deeper than point N, M experiences greater pressure due to the additional weight of water above it. The pressure difference equals ρg(0.20 m), where ρ is water density and g is gravitational acceleration. Choice B incorrectly suggests pressure decreases with depth, which violates basic fluid statics principles. When analyzing fluid pressure, remember that pressure always increases as you go deeper, regardless of the fluid type or container.

6

Two points are in the same still water column open to the atmosphere. Point A is $0.30,\text{m}$ below the surface and point B is $0.30,\text{m}$ below the surface but at a different horizontal location. Pressure is due to fluid depth. How do the pressures compare?

$P_A=P_B$, because pressure depends only on depth in a static fluid

Cannot be determined without the container’s shape

$P_A>P_B$, because A is directly under the surface

$P_A<P_B$, because B is farther from the container wall

Explanation

This question tests understanding that pressure depends only on depth in a static fluid. In any static fluid, pressure at a given depth is P = P₀ + ρgh, which depends only on the vertical depth h below the surface, not on horizontal position. Since both points A and B are at the same 0.30 m depth, they experience identical pressure regardless of their horizontal separation or position relative to container walls. This principle allows pressure to be transmitted equally throughout a fluid at the same depth. Choice A incorrectly suggests that being "directly under" matters, confusing vertical depth with horizontal position. When analyzing fluid pressure, only the vertical depth below the surface determines the pressure value.

7

An open container holds oil. Point R is $0.10,\text{m}$ below the oil surface; point S is $0.40,\text{m}$ below the surface. Pressure is due to fluid depth. Which point has greater pressure in the oil?

Point R, because it is closer to the surface

Point S, because pressure increases with depth

They are equal, because oil is less dense than water

They are equal, because the container could be wide or narrow

Explanation

This question tests understanding of pressure increasing with fluid depth. Pressure in a static fluid follows P = P₀ + ρgh, where ρ is the oil's density and h is depth. Point S at 0.40 m depth has four times the gauge pressure (ρgh) compared to Point R at 0.10 m depth, regardless of the oil's specific density. The absolute pressure includes atmospheric pressure P₀ at both points, but the pressure difference depends only on the depth difference. Choice D incorrectly implies that oil's lower density compared to water affects which point has higher pressure, when depth alone determines the ranking. For any fluid, deeper points have higher pressure following the same P = P₀ + ρgh relationship.

8

In a freshwater pool, pressure is due to fluid depth. Point $X$ is $1.5,\text{m}$ below the surface and point $Y$ is $0.5,\text{m}$ below. Which is correct?

The pressure depends on the pool’s width at each depth.

$p_X<p_Y$ because the higher point has more water above it.

$p_X=p_Y$ because water transmits pressure equally.

$p_X>p_Y$ because the deeper point has greater pressure.

Explanation

This question tests understanding of pressure variation with depth in fluids. In static fluids, pressure increases with depth according to P = P₀ + ρgh. Point X at 1.5 m depth has greater pressure than point Y at 0.5 m depth because X has more water weight above it. The pressure difference is ρg(1.5 - 0.5) = ρg(1.0 m). Choice A incorrectly reverses this relationship, perhaps misunderstanding which point is deeper. When comparing fluid pressures, always identify which point is deeper below the surface, as deeper points have higher pressure.

9

A $50,\text{N}$ block is placed on a table. Case 1 contact area is $0.005,\text{m}^2$; Case 2 contact area is $0.010,\text{m}^2$; pressure is due to contact force. Which case has greater pressure?

Case 1, because the same force acts on a smaller area

Cannot be determined without knowing the block’s shape

Case 2, because larger area means larger pressure

Same in both cases because the block’s weight is $50,\text{N}$

Explanation

This question tests understanding of pressure as force divided by contact area. The block's weight (50 N) creates the same downward force in both cases. Case 1: pressure = 50 N / 0.005 m² = 10,000 Pa. Case 2: pressure = 50 N / 0.010 m² = 5,000 Pa. Case 1 has twice the pressure because it has half the contact area. Choice A reverses the relationship, incorrectly thinking larger area means larger pressure when actually pressure and area are inversely related for constant force. To find pressure from contact forces, always divide the perpendicular force by the contact area.

10

A $300,\text{N}$ machine rests on four identical feet. Each foot has area $2.0\times10^{-3},\text{m}^2$; pressure is due to contact force. Compared to one foot supporting the full weight, the pressure is

four times smaller, because the force per foot is smaller while area per foot is the same

dependent on the spacing between the feet, not on force and area

four times larger, because there are four feet

the same, because the total weight is unchanged

Explanation

This question tests understanding of pressure distribution across multiple contact points. When the 300 N machine rests on four identical feet, each foot supports 300 N / 4 = 75 N. The pressure at each foot is P = 75 N / (2.0×10⁻³ m²) = 37,500 Pa. If one foot supported the full weight, pressure would be 300 N / (2.0×10⁻³ m²) = 150,000 Pa, which is four times larger. The four-foot configuration reduces pressure to one-fourth because each foot carries one-fourth the force while maintaining the same contact area. Choice A incorrectly multiplies by the number of feet. When weight is distributed across multiple supports, divide the total force by the number of supports to find force per support.

Page 1 of 5