| Step | Reasoning |
|---|---|
| Identify the relationship between height difference and pressure difference. \[P_1 = P_{atm} + \rho g h_1\] \[P_2 = P_{atm} + \rho g h_2\] \[P_1 – P_2 = \rho g (h_1 – h_2) = \rho g \Delta h\] |
The fluid in the vertical tubes is in static equilibrium with the pressure in the pipe at the attachment points. The height of the fluid column relates to the gauge pressure. |
| Use Bernoulli’s equation to relate the pressures in the two horizontal sections. \[P_1 + \dfrac{1}{2}\rho v_1^2 = P_2 + \dfrac{1}{2}\rho v_2^2\] \[P_1 – P_2 = \dfrac{1}{2}\rho (v_2^2 – v_1^2)\] |
Since the pipe is horizontal and the fluid is ideal and incompressible, Bernoulli’s principle relates the pressure and flow speed at any two points along a streamline. |
| Determine the speed of the fluid in Section 2 using the continuity equation. \[A_1 v_1 = A_2 v_2\] \[A(v) = \left(\dfrac{A}{3}\right)v_2\] \[v_2 = 3v\] |
The speed \(v_2\) is unknown, but the cross-sectional areas are given. For an incompressible fluid, the volume flow rate is constant. |
| Substitute the speeds back into the pressure equation and solve for the height difference. \[\rho g \Delta h = \dfrac{1}{2}\rho ((3v)^2 – v^2)\] \[\rho g \Delta h = \dfrac{1}{2}\rho (9v^2 – v^2)\] \[\rho g \Delta h = \dfrac{1}{2}\rho (8v^2)\] \[g \Delta h = 4v^2\] \[\Delta h = \dfrac{4v^2}{g}\] |
Combining the results from the previous steps allows us to express \(\Delta h\) in terms of the given variables and constants. |
Why each choice is correct or incorrect:
(A) This is the correct answer.
(B) Forgets the \(1/2\) coefficient in the Bernoulli terms: \(\Delta P = \rho (3v)^2 – \rho v^2 = 8\rho v^2\).
(C) Considers only the pressure drop due to the speed in Section 2, ignoring the initial kinetic energy density: \(\rho g \Delta h = \dfrac{1}{2}\rho (3v)^2 = \dfrac{9}{2}\rho v^2\).
(D) Reverses the continuity relationship, assuming speed is proportional to area rather than inversely proportional: \(v_2 = v/3\), leading to \(\Delta P = \dfrac{1}{2}\rho (v^2 – (v/3)^2) = \dfrac{4}{9}\rho v^2\).
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A hydraulic lift is constructed with an input cylinder of cross-sectional area \(A\) and an output cylinder of cross-sectional area \(4A\). The cylinders are filled with an incompressible fluid of density \(\rho\). Initially, the system is in equilibrium with the fluid at the same horizontal level in both cylinders. A crate of mass \(M\) is placed on the output piston, and an external force \(F\) is applied to the input piston to lift the crate. The crate is raised a vertical distance \(h\) and then held at rest. Assuming the pistons have negligible mass and the fluid is ideal, which of the following is a correct expression for the magnitude of the force \(F\) required to hold the crate in this new position?

An ideal, incompressible fluid flows at a steady rate through a horizontal, cylindrical pipe. At Section A, the pipe has a radius \(R\). Further downstream, at Section B, the pipe narrows to a radius \(\frac{R}{2}\). Which of the following correctly compares the fluid speed \(v\), the volume flow rate \(Q\), and the time \(\Delta t\) required for a fixed volume of fluid to pass through a cross-sectional plane at Section B to the corresponding values at Section A?

A ship of mass \(M\) floats in equilibrium in a body of water with density \(\rho_w\). The ship has a flat-bottomed hull with a constant horizontal cross-sectional area \(A\). The bottom of the hull is submerged to a depth \(h\) below the surface, and the atmospheric pressure is \(P_{atm}\). Two students make the following claims about the forces acting on the ship:
Student 1: The buoyant force exerted by the water is equal to the weight of the displaced water, \(\rho_w Ahg\), and this force must be equal to the ship’s weight, \(Mg\).
Student 2: The upward force from the water on the bottom of the hull is what supports the ship, so the water pressure at the depth of the hull’s bottom must be equal to \(\dfrac{Mg}{A}\).
Which student’s claim is correct, and what is the valid physical justification?

A diving bell is lowered from the surface of a deep lake into the water at a constant speed \(v\). At the surface of the lake, the absolute pressure is \(P_{atm}\). The bell is lowered until the absolute pressure exerted by the water on the bell is \(1.5 P_{atm}\), which occurs at time \(t_1\) after the bell leaves the surface. At what time \(t_2\) after leaving the surface will the absolute pressure on the bell be \(2.5 P_{atm}\)?

A hydraulic lift is filled with an ideal, incompressible fluid of negligible mass. A car of mass \( M \) sits on a large circular piston of radius \( R \). A mechanic applies a constant downward force \( F \) to a smaller circular piston of radius \( r \), causing the car to be lifted a vertical distance \( H \) at a constant speed. Which of the following correctly identifies the magnitude of the force \( F \) and the total work \( W \) done by the mechanic on the system?

Three containers with the same base area \(A\) are filled with the same liquid of density \(\rho\) to the same height \(h\). Container 1 is a cylinder, Container 2 has walls that narrow toward the top, and Container 3 has walls that widen toward the top, as shown in the diagram. Which of the following correctly compares the magnitude of the downward force \(F_{base}\) exerted by the liquid on the base of Container 3 to the weight \(W\) of the liquid in Container 3, and provides a correct justification?

A rigid object with a volume \(V\) is fully submerged and held at a fixed position in a horizontal pipe. The object has an asymmetrical cross-section that is flat on the bottom and curved on the top. In Situation 1, the water in the pipe is stationary. In Situation 2, water of density \(\rho\) flows through the pipe at a high constant velocity. In both situations, the object is completely surrounded by water and remains at the same depth. Which of the following correctly compares the magnitude of the net vertical force \(F_{\text{water}}\) exerted by the water on the object in the two situations and provides a correct physical justification?

A uniform horizontal rod of mass \(M\) and length \(L\) is supported by a pivot located at a distance \(L/4\) from its left end. A small block of mass \(m_1\) is suspended from the left end of the rod. At the right end of the rod, a string is attached to a solid object of volume \(V\) and density \(\rho_s\). The object is fully submerged in a container of liquid with density \(\rho_f\), where \(\rho_s > \rho_f\). If the system is in static equilibrium with the rod remaining horizontal, which of the following is a correct expression for the mass \(m_1\)?

In a water filtration system, water flows through a main horizontal pipe of diameter \(D_1\) with a constant speed \(v_1\). To increase the speed for the filtration process, the pipe tapers to a smaller diameter \(D_2\). Assuming the water behaves as an ideal, incompressible fluid, which of the following expressions correctly represents the speed \(v_2\) of the water in the narrower section of the pipe?

Sphere 1 has mass \(M\) and volume \(V\). When placed in a large tank of water, it floats at rest with exactly half of its volume submerged. Sphere 2 has mass \(3M\) and the same volume \(V\). When Sphere 2 is placed in the same tank, it sinks to the bottom and remains at rest. Which of the following correctly compares the magnitude of the buoyant force \(F_{B1}\) on Sphere 1 and the magnitude of the buoyant force \(F_{B2}\) on Sphere 2?
A
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| Kinematics | Forces |
|---|---|
| \(\Delta x = v_i t + \frac{1}{2} at^2\) | \(F = ma\) |
| \(v = v_i + at\) | \(F_g = \frac{G m_1 m_2}{r^2}\) |
| \(v^2 = v_i^2 + 2a \Delta x\) | \(f = \mu N\) |
| \(\Delta x = \frac{v_i + v}{2} t\) | \(F_s =-kx\) |
| \(v^2 = v_f^2 \,-\, 2a \Delta x\) |
| Circular Motion | Energy |
|---|---|
| \(F_c = \frac{mv^2}{r}\) | \(KE = \frac{1}{2} mv^2\) |
| \(a_c = \frac{v^2}{r}\) | \(PE = mgh\) |
| \(T = 2\pi \sqrt{\frac{r}{g}}\) | \(KE_i + PE_i = KE_f + PE_f\) |
| \(W = Fd \cos\theta\) |
| Momentum | Torque and Rotations |
|---|---|
| \(p = mv\) | \(\tau = r \cdot F \cdot \sin(\theta)\) |
| \(J = \Delta p\) | \(I = \sum mr^2\) |
| \(p_i = p_f\) | \(L = I \cdot \omega\) |
| Simple Harmonic Motion | Fluids |
|---|---|
| \(F = -kx\) | \(P = \frac{F}{A}\) |
| \(T = 2\pi \sqrt{\frac{l}{g}}\) | \(P_{\text{total}} = P_{\text{atm}} + \rho gh\) |
| \(T = 2\pi \sqrt{\frac{m}{k}}\) | \(Q = Av\) |
| \(x(t) = A \cos(\omega t + \phi)\) | \(F_b = \rho V g\) |
| \(a = -\omega^2 x\) | \(A_1v_1 = A_2v_2\) |
| Constant | Description |
|---|---|
| [katex]g[/katex] | Acceleration due to gravity, typically [katex]9.8 , \text{m/s}^2[/katex] on Earth’s surface |
| [katex]G[/katex] | Universal Gravitational Constant, [katex]6.674 \times 10^{-11} , \text{N} \cdot \text{m}^2/\text{kg}^2[/katex] |
| [katex]\mu_k[/katex] and [katex]\mu_s[/katex] | Coefficients of kinetic ([katex]\mu_k[/katex]) and static ([katex]\mu_s[/katex]) friction, dimensionless. Static friction ([katex]\mu_s[/katex]) is usually greater than kinetic friction ([katex]\mu_k[/katex]) as it resists the start of motion. |
| [katex]k[/katex] | Spring constant, in [katex]\text{N/m}[/katex] |
| [katex] M_E = 5.972 \times 10^{24} , \text{kg} [/katex] | Mass of the Earth |
| [katex] M_M = 7.348 \times 10^{22} , \text{kg} [/katex] | Mass of the Moon |
| [katex] M_M = 1.989 \times 10^{30} , \text{kg} [/katex] | Mass of the Sun |
| Variable | SI Unit |
|---|---|
| [katex]s[/katex] (Displacement) | [katex]\text{meters (m)}[/katex] |
| [katex]v[/katex] (Velocity) | [katex]\text{meters per second (m/s)}[/katex] |
| [katex]a[/katex] (Acceleration) | [katex]\text{meters per second squared (m/s}^2\text{)}[/katex] |
| [katex]t[/katex] (Time) | [katex]\text{seconds (s)}[/katex] |
| [katex]m[/katex] (Mass) | [katex]\text{kilograms (kg)}[/katex] |
| Variable | Derived SI Unit |
|---|---|
| [katex]F[/katex] (Force) | [katex]\text{newtons (N)}[/katex] |
| [katex]E[/katex], [katex]PE[/katex], [katex]KE[/katex] (Energy, Potential Energy, Kinetic Energy) | [katex]\text{joules (J)}[/katex] |
| [katex]P[/katex] (Power) | [katex]\text{watts (W)}[/katex] |
| [katex]p[/katex] (Momentum) | [katex]\text{kilogram meters per second (kgm/s)}[/katex] |
| [katex]\omega[/katex] (Angular Velocity) | [katex]\text{radians per second (rad/s)}[/katex] |
| [katex]\tau[/katex] (Torque) | [katex]\text{newton meters (Nm)}[/katex] |
| [katex]I[/katex] (Moment of Inertia) | [katex]\text{kilogram meter squared (kgm}^2\text{)}[/katex] |
| [katex]f[/katex] (Frequency) | [katex]\text{hertz (Hz)}[/katex] |
Metric Prefixes
Example of using unit analysis: Convert 5 kilometers to millimeters.
Start with the given measurement: [katex]\text{5 km}[/katex]
Use the conversion factors for kilometers to meters and meters to millimeters: [katex]\text{5 km} \times \frac{10^3 \, \text{m}}{1 \, \text{km}} \times \frac{10^3 \, \text{mm}}{1 \, \text{m}}[/katex]
Perform the multiplication: [katex]\text{5 km} \times \frac{10^3 \, \text{m}}{1 \, \text{km}} \times \frac{10^3 \, \text{mm}}{1 \, \text{m}} = 5 \times 10^3 \times 10^3 \, \text{mm}[/katex]
Simplify to get the final answer: [katex]\boxed{5 \times 10^6 \, \text{mm}}[/katex]
Prefix | Symbol | Power of Ten | Equivalent |
|---|---|---|---|
Pico- | p | [katex]10^{-12}[/katex] | 0.000000000001 |
Nano- | n | [katex]10^{-9}[/katex] | 0.000000001 |
Micro- | µ | [katex]10^{-6}[/katex] | 0.000001 |
Milli- | m | [katex]10^{-3}[/katex] | 0.001 |
Centi- | c | [katex]10^{-2}[/katex] | 0.01 |
Deci- | d | [katex]10^{-1}[/katex] | 0.1 |
(Base unit) | – | [katex]10^{0}[/katex] | 1 |
Deca- or Deka- | da | [katex]10^{1}[/katex] | 10 |
Hecto- | h | [katex]10^{2}[/katex] | 100 |
Kilo- | k | [katex]10^{3}[/katex] | 1,000 |
Mega- | M | [katex]10^{6}[/katex] | 1,000,000 |
Giga- | G | [katex]10^{9}[/katex] | 1,000,000,000 |
Tera- | T | [katex]10^{12}[/katex] | 1,000,000,000,000 |
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