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| Step | Derivation/Formula | Reasoning |
|---|---|---|
| 1. Sum of Forces in the Horizontal Direction (x-axis) | \[ \sum F_x = 0 \implies N_1 – f = 0 \implies N_1 = f \] | Horizontal forces balance; friction equals wall’s normal force. |
| 2. Sum of Forces in the Vertical Direction (y-axis) | \[ \sum F_y = 0 \implies N_2 – m_1 g – m_2 g = 0 \implies N_2 = (m_1 + m_2) g \] | Vertical forces balance; ground’s normal force equals total weight. |
| 3. Sum of Torques About the Bottom of the Ladder | \[ N_1 L \sin \theta – m_1 g d \cos \theta – m_2 g \left( \dfrac{L}{2} \cos \theta \right) = 0 \] \[ N_1 = \dfrac{m_1 g d + \dfrac{1}{2} m_2 g L}{L \tan \theta} \] | Set net torque to zero; solve for \( N_1 \). |
| 4. Frictional Force at the Point of Slipping | \[ f_{\text{max}} = \mu_{\text{min}} N_2 = \mu_{\text{min}} (m_1 + m_2) g \] \[ N_1 = f = \mu_{\text{min}} (m_1 + m_2) g \] | Relate friction to normal force and coefficient of friction. |
| 5. Solving for \( \mu_{\text{min}} \) | \[ \mu_{\text{min}} (m_1 + m_2) g = \dfrac{m_1 g d + \dfrac{1}{2} m_2 g L}{L \tan \theta} \] \[ \mu_{\text{min}} = \dfrac{m_1 d + \dfrac{1}{2} m_2 L}{(m_1 + m_2) L \tan \theta} \] | Equate expressions for \( N_1 \) and solve for \( \mu_{\text{min}} \). |
| 6. Answer to First Part | \[ \mu_{\text{min}} = \dfrac{m_1 d + \dfrac{1}{2} m_2 L}{(m_1 + m_2) L \tan \theta} \] | Minimum coefficient of static friction required. |
| 7. Given \( \mu_s = \dfrac{3}{2} \mu_{\text{min}} \) | \[ \mu_s = \dfrac{3}{2} \mu_{\text{min}} \] | Actual coefficient of friction is 1.5 times \( \mu_{\text{min}} \). |
| 8. Calculating Frictional Force \( f \) | \[ f = N_1 = \mu_{\text{min}} (m_1 + m_2) g \] | Frictional force required for equilibrium. |
| 9. Answer to Second Part | \[ f = \mu_{\text{min}} (m_1 + m_2) g \] | Magnitude of frictional force with increased \( \mu_s \). |
Just ask: "Help me solve this problem."
A wheel of radius R and negligible mass is mounted on a horizontal frictionless axle so that the wheel is in a vertical plane. Three small objects having masses [katex]m[/katex], [katex]M[/katex], and [katex]2M[/katex], respectively, are mounted on the rim of the wheel, as shown above. If the system is in static equilibrium, what is the value of [katex]m[/katex] in terms of [katex]M[/katex] ?
An object is experiencing a nonzero net force. Which of the following statements is most accurate?
The downward motion of an elevator is controlled by a cable that unwinds from a cylinder of radius \( 0.20 \) \( \text{m} \). What is the angular velocity of the cylinder when the downward speed of the elevator is \( 1.2 \) \( \text{m/s} \)?
A disk, a hoop, and a solid sphere are released at the same time at the top of an inclined plane. They are all uniform and roll without slipping. In what order do they reach the bottom?
\( \text{Solid sphere: } I = \frac{2}{5}mR^2, \quad \text{Solid disk: } I = \frac{1}{2}mR^2, \quad \text{Hoop: } I = mR^2 \)
1. \( \mu_{\text{min}} = \dfrac{m_1 d + \dfrac{1}{2} m_2 L}{(m_1 + m_2) L \tan \theta} \)
2. \( f = \mu_{\text{min}} (m_1 + m_2) g \)
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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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