AP Physics

Unit 5 - Linear Momentum

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Part (a) Post-collision velocity

Step Derivation / Formula Reasoning
1 \[m_b v_i = (m_b + M) v_x\] Linear momentum of the bullet–block system is conserved because the external horizontal forces are negligible. Here \(m_b\) is the bullet mass, \(M\) the block mass, \(v_i\) the bullet’s initial speed, and \(v_x\) the common speed just after impact.
2 \[v_x = \frac{m_b v_i}{m_b + M}\] Algebraically solve the previous relation for the unknown \(v_x\).
3 \[v_x = \frac{0.0500\,\text{kg}\,\times\,50.0\,\text{m/s}}{0.0500\,\text{kg}+0.300\,\text{kg}} = 7.14\,\text{m/s}\] Substitute the given numerical values: \(m_b = 0.0500\,\text{kg}\), \(M = 0.300\,\text{kg}\), and \(v_i = 50.0\,\text{m/s}\).
4 \[\boxed{v_x = 7.14\,\text{m/s}}\] State the final speed of the combined mass immediately after the collision.

Part (b) Rise height

Step Derivation / Formula Reasoning
1 \[\tfrac12 (m_b+M) v_x^2 = (m_b+M) g h\] After impact, kinetic energy converts into gravitational potential energy at the highest point; mechanical energy is conserved because non-conservative work is negligible.
2 \[h = \frac{v_x^2}{2g}\] Solve the energy equation for vertical rise \(h\); the common mass cancels out.
3 \[h = \frac{(7.14\,\text{m/s})^2}{2\,(9.80\,\text{m/s}^2)} = 2.60\,\text{m}\] Insert \(v_x = 7.14\,\text{m/s}\) and \(g = 9.80\,\text{m/s}^2\) to compute the height.
4 \[\boxed{h = 2.60\,\text{m}}\] Quote the vertical distance the system rises.

Part (c) Effect comparison

Step Derivation / Formula Reasoning
1 \[h = \frac{(m_b v_i)^2}{2g\,(m_b+M)^2}\] Combine momentum \(m_b v_i=(m_b+M)v_x\) with energy \(h=v_x^2/2g\) to express \(h\) only in terms of parameters \(m_b\) and \(v_i\).
2 \[h’_v = 4h\] Doubling \(v_i\) multiplies the numerator of the above expression by \(2^2=4\), while the denominator is unchanged; thus height becomes four times larger.
3 \[\frac{h’_m}{h}=4\left(\frac{m_b+M}{2m_b+M}\right)^2\] Replacing \(m_b\) by \(2m_b\) changes both numerator and denominator; the ratio displayed compares the new height to the original.
4 \[\frac{h’_m}{h}=3.06\,\text{(for given masses)}\] With \(m_b=0.0500\,\text{kg}\) and \(M=0.300\,\text{kg}\), doubling mass raises height by a factor \(3.06<4\).
5 \[\boxed{\text{Doubling }v_i\text{ increases }h\text{ the most}}\] Because height depends on the square of speed but less strongly on bullet mass, option (i) has the greater effect; option (iii) is therefore false.

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\(7.14\,\text{m/s}\)
\(2.60\,\text{m}\)
\(\text{Doubling bullet’s velocity}\)

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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]

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