AP Physics

Unit 1 - Vectors and Kinematics

Intermediate

Mathematical

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Part (a): Time Interval When Object Passes Through Initial Position

Step Derivation/Formula Reasoning
1 \(v(t) = \text{Area under velocity-time graph}\) Object passes through its initial position when the net area under the velocity-time graph (Displacement, \( \Delta x \)) is zero.
2 N/A (Graph Inspection) From \( t = 0 \, \text{s} \) to \( t = 5 \, \text{s} \), the area under the curve is a triangle with base 5 s and height 20 m/s giving an area of \( \frac{1}{2} \times 5 \, \text{s} \times 20 \, \text{m/s} = 50 \, \text{m} \).
3 N/A (Graph Inspection) From \( t = 5 \, \text{s} \) to \( t = 11 \, \text{s} \), the area under the curve is a large negative area as shown in the graph. Calculate areas to compensate for positive 50 m.
4 N/A (Graph Inspection) The area from \( t = 5 \, \text{s} \) to \( t = 8 \, \text{s} \) is -40, while the area from \( t = 5 \, \text{s} \) to \( t = 9 \, \text{s} \) is -60 m.
5 Conclusion Between 8 to 9 seconds the area, representing displacement, reaches \( -50 \, \text{m} \), which would cancel out the \( +50 \, \text{m} \) covered in the first 5 seconds. Thus, between 8 and 9 seconds, displacement is 0, which means the particle is back to its original starting point.

Part (b): Same Average Acceleration Interval as \(12 \, \text{s} < t < 14 \, \text{s}\)

Step Derivation/Formula Reasoning
1 \(\text{Average acceleration} = \frac{\Delta v}{\Delta t}\) The average acceleration is the change in velocity divided by the change in time (the slope of the graph)
2 \(\Delta v = v_f – v_i = 0 – 0 \, \text{m/s} = 0 \, \text{m/s}\) The change in velocity for \(12 \, \text{s} < t < 14 \, \text{s}\) is \( \Delta v = 0 \, \text{m/s}\).
3 \(\Delta t = 14 \, \text{s} – 12 \, \text{s} = 2 \, \text{s}\) The time interval is \( \Delta t = 2 \, \text{s}\).
4 \(\text{Average acceleration} = \frac{0 \, \text{m/s}}{2 \, \text{s}}\) Substitute the values obtained for \( \Delta v \) and \( \Delta t \).
5 \(\text{Average acceleration} = 0 \, \text{m/s}^2\) The average acceleration for \(12 \, \text{s} < t < 14 \, \text{s}\) is \( 0 \, \text{m/s}^2\).
6 Find the identical slope on a different part of of the graph. The interval from \( 7 \, \text{s} \) to \( 10 \, \text{s} \) also shows 0 slope resulting in same acceleration.

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KinematicsForces
\(\Delta x = v_i t + \frac{1}{2} at^2\)\(F = ma\)
\(v = v_i + at\)\(F_g = \frac{G m_1 m_2}{r^2}\)
\(v^2 = v_i^2 + 2a \Delta x\)\(f = \mu N\)
\(\Delta x = \frac{v_i + v}{2} t\)\(F_s =-kx\)
\(v^2 = v_f^2 \,-\, 2a \Delta x\) 
Circular MotionEnergy
\(F_c = \frac{mv^2}{r}\)\(KE = \frac{1}{2} mv^2\)
\(a_c = \frac{v^2}{r}\)\(PE = mgh\)
\(T = 2\pi \sqrt{\frac{r}{g}}\)\(KE_i + PE_i = KE_f + PE_f\)
 \(W = Fd \cos\theta\)
MomentumTorque 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 MotionFluids
\(F = -kx\)\(P = \frac{F}{A}\)
\(T = 2\pi \sqrt{\frac{l}{g}}\)\(P_{\text{total}} = P_{\text{atm}} + \rho gh\)
\(T = 2\pi \sqrt{\frac{m}{k}}\)\(Q = Av\)
\(x(t) = A \cos(\omega t + \phi)\)\(F_b = \rho V g\)
\(a = -\omega^2 x\)\(A_1v_1 = A_2v_2\)
ConstantDescription
[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
VariableSI 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]
VariableDerived 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. 

  1. Start with the given measurement: [katex]\text{5 km}[/katex]

  2. 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]

  3. 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]

  4. 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]

  1. 1. Some answers may vary by 1% due to rounding.
  2. Gravity values may differ: \(9.81 \, \text{m/s}^2\) or \(10 \, \text{m/s}^2\).
  3. Variables can be written differently. For example, initial velocity (\(v_i\)) may be \(u\), and displacement (\(\Delta x\)) may be \(s\).
  4. Bookmark questions you can’t solve to revisit them later
  5. 5. Seek help if you’re stuck. The sooner you understand, the better your chances on tests.

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