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Part A – Buoyant force
| Step | Derivation/Formula | Reasoning |
|---|---|---|
| (a) 1 | \(B = W_{\text{air}} – W_{\text{water}}\) | The buoyant force \(B\) equals the difference between the weight of the object measured in air and the apparent weight when submerged. |
| (a) 2 | \(B = 17.8\,N – 16.2\,N = 1.6\,N\) | Substitute the given readings to calculate the buoyant force. |
| (a) 3 | \(\boxed{B = 1.6\,N}\) | This is the final buoyant force acting on the object in water. |
Part B – Volume of the object
| Step | Derivation/Formula | Reasoning |
|---|---|---|
| (b) 1 | \(B = \rho_{w} g V\) | According to Archimedes’ principle, the buoyant force is equal to the weight of the displaced water where \(\rho_{w}\) is the density of water, \(g\) is gravitational acceleration, and \(V\) is the volume displaced. |
| (b) 2 | \(V = \frac{B}{\rho_{w} g}\) | Rearrange the formula to solve for the volume of the object. |
| (b) 3 | \(V = \frac{1.6}{1000 \times 9.8}\) | Substitute \(B = 1.6\,N\), \(\rho_{w} = 1000\,kg/m^3\), and \(g = 9.8\,m/s^2\). |
| (b) 4 | \(V \approx 1.63 \times 10^{-4}\,m^3\) | Compute the division \(1.6/(9800)\) to obtain the object’s volume. |
| (b) 5 | \(\boxed{V \approx 1.63 \times 10^{-4}\,m^3}\) | This is the final volume of the object. |
Part C – Density of the object
| Step | Derivation/Formula | Reasoning |
|---|---|---|
| (c) 1 | \(W = m g\) | The weight of the object in air is the product of its mass \(m\) and gravitational acceleration \(g\). |
| (c) 2 | \(m = \frac{W}{g} = \frac{17.8}{9.8}\) | Solve for the mass by rearranging the weight formula using \(W = 17.8\,N\) and \(g = 9.8\,m/s^2\). |
| (c) 3 | \(m \approx 1.82\,kg\) | Performing the division gives the mass of the object. |
| (c) 4 | \(\rho = \frac{m}{V}\) | Density is defined as mass divided by volume. |
| (c) 5 | \(\rho = \frac{1.82}{1.63 \times 10^{-4}}\) | Substitute \(m \approx 1.82\,kg\) and \(V \approx 1.63 \times 10^{-4}\,m^3\) into the density formula. |
| (c) 6 | \(\rho \approx 1.12 \times 10^4\,kg/m^3\) | The division yields the density of the object. |
| (c) 7 | \(\boxed{\rho \approx 1.12 \times 10^4\,kg/m^3}\) | This is the final density of the object. |
Part D – Absolute pressure when object is removed
| Step | Derivation/Formula | Reasoning |
|---|---|---|
| (d) 1 | \(p = p_{\text{atm}} + \rho_{w} g h\) | The absolute pressure at the bottom of a water column is given by the sum of atmospheric pressure \(p_{\text{atm}}\) and the hydrostatic pressure \(\rho_{w} g h\), where \(h\) is the water depth. |
| (d) 2 | Removing the object | Upon removal of the object, the water can now fill the space the ball occupied. This reduces the overall water depth \(h\). |
| (d) 4 | \(\boxed{p \text{ decreases}}\) | Thus, the hydrostatic pressure (\(\rho gh\)) decreases, due to the decrease in height of the water. Since hydrostatic pressure drops so will the absolute pressure, as given by the equation in (d) 1 |
Just ask: "Help me solve this problem."
Water flowing in a horizontal pipe speeds up as it goes from a section with a large diameter to a section with a small diameter. Which of the following can explain why the speed of the water increases?
A geologist suspects that her rock specimen is hollow, so she weighs the specimen in both air and water. When completely submerged, the rock weighs twice as much in air as it does in water.
Johnny the auto mechanic is raising a \( 1200 \) \( \text{kg} \) car on her hydraulic lift so that she can work underneath. If the area of the input piston is \( 12 \) \( \text{cm}^2 \), 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?
A beaker weighing \( 2.0 \) \( \text{N} \) is filled with \( 5.0 \times 10^{-3} \) \( \text{m}^3 \) of water. A rubber ball weighing \( 3.0 \) \( \text{N} \) is held entirely underwater by a massless string attached to the bottom of the beaker, as represented in the figure above. The tension in the string is \( 4.0 \) \( \text{N} \). The water fills the beaker to a depth of \( 0.20 \) \( \text{m} \). Water has a density of \( 1000 \) \( \text{kg/m}^3 \). The effects of atmospheric pressure may be neglected.
A block of weight \( W \) is floating in water, and one-third of the block is above the surface of the water. Which of the following correctly describes the magnitude \( F \) of the force that the block exerts on the water and explains why \( F \) has that value?
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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] |
General Metric Conversion Chart
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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