| Step | Derivation/Formula | Reasoning |
|---|---|---|
| Part (a): Total Time to Reach 80 m | ||
| 1 | \[ t_{a} = \frac{v_x-0}{0.10} = \frac{2.0}{0.10} = 20\;\text{s} \] | Calculate the time required to reach a speed of \(2.0\;\text{m/s}\) from rest with a constant acceleration \(0.10\;\text{m/s}^2\). |
| 2 | \[ \Delta x_{a} = \frac{1}{2}(0.10)(20)^2 = 20\;\text{m} \] | Determine the displacement during the acceleration phase using the uniform acceleration equation. |
| 3 | \[ \Delta x_{c} = 80\;\text{m} – 20\;\text{m} = 60\;\text{m} \] | Find the remaining distance after the acceleration phase for which the rig travels at constant speed. |
| 4 | \[ t_{c} = \frac{60\;\text{m}}{2.0\;\text{m/s}} = 30\;\text{s} \] | Compute the time taken during the constant speed phase using \(\Delta x=t\,v_x\). |
| 5 | \[ T = t_{a} + t_{c} = 20\;\text{s} + 30\;\text{s} = 50\;\text{s} \] | Sum the two time intervals to get the total time to 80 m depth. |
| 6 | \[ \boxed{50\;\text{s}} \] | This is the total descent time to reach the maximum depth. |
| Part (b): Weight of the Water on the Top of the Bell | ||
| 1 | \[ \Delta P = \rho g h = 1025\;\text{kg/m}^3 \times 9.8\;\text{m/s}^2 \times 80\;\text{m} \] | Compute the hydrostatic pressure due to an 80 m water column (excluding the 1 atm inside the bell). |
| 2 | \[ \Delta P \approx 1025 \times 9.8 \times 80 \approx 803600\;\text{Pa} \] | Evaluate the product to obtain the pressure increase from the water column. |
| 3 | \[ F = \Delta P \times A = 803600\;\text{Pa} \times 9.0\;\text{m}^2 \] | Calculate the force (i.e. the weight of the water) on the bell’s top using its cross-sectional area. |
| 4 | \[ F \approx 7.2324 \times 10^6\;\text{N} \] | Multiply to get the force in newtons. |
| 5 | \[ \boxed{7.23 \times 10^6\;\text{N}} \] | This is the weight of the water exerted on the top of the bell at 80 m depth. |
| Part (c): Absolute Pressure on the Top of the Bell | ||
| 1 | \[ P_{\text{abs}} = P_{\text{atm}} + \rho g h \] | Add the atmospheric pressure at the surface to the hydrostatic pressure due to the 80 m water column. |
| 2 | \[ P_{\text{abs}} = 101325\;\text{Pa} + 803600\;\text{Pa} \] | Use \(101325\;\text{Pa}\) for 1 atm and the hydrostatic pressure found earlier. |
| 3 | \[ P_{\text{abs}} \approx 904925\;\text{Pa} \] | Sum the pressures to get the absolute pressure at depth. |
| 4 | \[ \boxed{9.05 \times 10^5\;\text{Pa}} \] | This is the absolute pressure on the top of the bell at 80 m depth. |
| Part (d): Minimum Force to Lift the Hatch | ||
| 1 | \[ A_{h} = \pi r^2 = \pi (0.25)^2 = \pi (0.0625) \approx 0.19635\;\text{m}^2 \] | Determine the area of the circular hatch with radius \(r = 0.25\;\text{m}\). |
| 2 | \[ F_{h} = \Delta P \times A_{h} = 803600\;\text{Pa} \times 0.19635\;\text{m}^2 \] | Calculate the net force acting on the hatch due to the pressure difference (\(\Delta P\)) computed earlier. |
| 3 | \[ F_{h} \approx 157800\;\text{N} \] | Multiply to find the minimum force necessary to overcome the water pressure on the hatch. |
| 4 | \[ \boxed{1.58 \times 10^5\;\text{N}} \] | This is the minimum force required to start lifting the hatch at the maximum depth. |
| Part (e): Reducing the Force to Open the Hatch | ||
| 1 | N/A | The force to open the hatch is given by the pressure difference multiplied by its area. To reduce this force, the net pressure difference must be decreased. |
| 2 | N/A | One effective method is to equalize the pressure on both sides of the hatch by increasing the internal pressure of the bell (for example, via a pressure equalization valve or controlled venting) so that it approaches the external hydrostatic pressure. |
| 3 | N/A | This reduces the differential pressure \(\Delta P\) acting on the hatch, thereby lowering the force required to open it. |
| 4 | N/A | Alternatively, decreasing the hatch area would also reduce the force, but modifying the pressure is generally more practical. |
| 5 | Answer: | To reduce the force, increase the bell’s internal pressure to nearly match the external pressure (or use a pressure equalization system), which minimizes the net pressure difference on the hatch. |
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The large piston in a hydraulic lift has a radius of \( 250 \) \( \text{cm}^2 \). What force must be applied to the small piston with a radius of \( 25 \) \( \text{cm}^2 \) in order to raise a car of mass \( 1500 \) \( \text{kg} \)?
In a town’s water system, pressure gauges in still water at street level read \( 150 \) \( \text{kPa} \). If a pipeline connected to the system breaks and shoots water straight up, how high above the street does the water shoot?
A sphere of mass \(0.5\) \(\text{kg}\) is dropped into a column of oil. At the instant the sphere becomes completely submerged in the oil, the sphere is moving downward at \(8\) \(\text{m/s}\), the buoyancy force on the sphere is \(4.0\) \(\text{N}\), and the fluid frictional force is \(4.0\) \(\text{N}\). Which of the following describes the motion of the sphere at this instant?
In the lab, a student is given a glass beaker filled with water with an ice cube of mass \( m \) and volume \( V_c \) floating in it.
The downward force of gravity on the ice cube has magnitude \( F_g \). The student pushes down on the ice cube with a force of magnitude \( F_P \) so that the cube is totally submerged. The water then exerts an upward buoyant force on the ice cube of magnitude \( F_B \). Which of the following is an expression for the magnitude of the acceleration of the ice cube when it is released?
A cube of side length \( s \) rests on the bottom surface of a container of fluid. The fluid is at a height \( y \) above the bottom of the tank. The fluid has density \( \rho \) and the atmospheric pressure is \( P_{\text{atm}} \).
Which of the following expressions is equal to the absolute pressure exerted by the fluid on the top surface of the cube?
An object is suspended from a spring scale first in air, then in water, as shown in the figure above. The spring scale reading in air is \( 17.8 \) \( \text{N} \), and the spring scale reading when the object is completely submerged in water is \( 16.2 \) \( \text{N} \). The density of water is \( 1000 \) \( \text{kg/m}^3 \).
Rex, an auto mechanic, is raising a \( 1200 \) \( \text{kg} \) car on his hydraulic lift so that he can work underneath. If the area of the input piston is \( 12.0 \) \( \text{cm}^2 \), while the output piston has an area of \( 700 \) \( \text{cm}^2 \), what force must be exerted on the input piston to lift the car?
You have a giant cask of water with a spigot some height below the water surface. The surface of the water, which is essentially at rest, is exposed to atmosphere (\( \approx 10^5 \text{Pa} \)). The water density is \( \approx 1000 \text{kg/m}^3 \). The water pours out of the spigot at \( 3 \text{m/s} \). How far below the water surface is the spigot positioned?
Water circulates throughout a house in a hot water heating system. If the water is pumped at a speed of \( 0.5 \) \( \frac{\text{m}}{\text{s}} \) through a \( 2 \) \( \text{cm} \) diameter pipe in the basement under a pressure of \( 3 \) \( \text{atm} \), what will be the flow speed and pressure in a \( 1.3 \) \( \text{cm} \) diameter pipe on the second floor \( 5 \) \( \text{m} \) above?
The figure shows a horizontal pipe with sections with different cross-sectional areas. Small tubes extend from the top of each section. The cross-sectional area of the pipe at location C is half that at A, and the areas at A and D are the same. Water flows in the pipe from left to right. Which of the following correctly ranks the height \( h \) of the water in the tubes above the labeled locations?
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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] | |
Nano- | n | [katex]10^{-9}[/katex] | |
Micro- | µ | [katex]10^{-6}[/katex] | |
Milli- | m | [katex]10^{-3}[/katex] | |
Centi- | c | [katex]10^{-2}[/katex] | |
Deci- | d | [katex]10^{-1}[/katex] | |
(Base unit) | – | [katex]10^{0}[/katex] | |
Deca- or Deka- | da | [katex]10^{1}[/katex] | |
Hecto- | h | [katex]10^{2}[/katex] | |
Kilo- | k | [katex]10^{3}[/katex] | |
Mega- | M | [katex]10^{6}[/katex] | |
Giga- | G | [katex]10^{9}[/katex] | |
Tera- | T | [katex]10^{12}[/katex] |
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