Physics Chapter: Motion and Forces

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Questions and Answers

What characterizes the magnetic field inside a solenoid?

  • It decreases exponentially with the distance from the center.
  • It is uniform and proportional to the number of turns per unit length and current. (correct)
  • It is non-uniform and depends on the square of the current.
  • It varies linearly with distance from the center.

A wire carrying current $I$ with length vector $\vec{L}$ is placed in a magnetic field $\vec{B}$. Which of the following represents the force $\vec{F}$ on the wire?

  • $\vec{F} = q\vec{v} \times \vec{B}$
  • $\vec{F} = q \vec{E}$
  • $\vec{F} = I \vec{B} \times \vec{L}$
  • $\vec{F} = I \vec{L} \times \vec{B}$ (correct)

According to Faraday's law of induction, what induces an electric field?

  • A static electric charge.
  • A constant magnetic field.
  • A uniform electric field.
  • A changing magnetic flux. (correct)

In an AC circuit, how does the current relate to the voltage across a capacitor?

<p>The current leads the voltage by $90^\circ$. (C)</p> Signup and view all the answers

Which phenomenon demonstrates the wave property of light?

<p>Young's double-slit experiment. (A)</p> Signup and view all the answers

What does the vector product $\vec{\omega} \times \vec{r}$ represent in the context of a point-like object rotating about an axis?

<p>The linear velocity of the object. (B)</p> Signup and view all the answers

In multi-dimensional motion, which of the following expressions correctly represents the acceleration vector $\vec{a}(t)$?

<p>$\vec{a}(t) = \frac{d\vec{v}}{dt}$ (A)</p> Signup and view all the answers

According to Newton's First Law, what condition ensures an object remains in uniform motion?

<p>The object is not subjected to any external forces. (B)</p> Signup and view all the answers

If the net force acting on an object is zero, what does Newton's Second Law imply about the object's acceleration?

<p>The acceleration is zero. (D)</p> Signup and view all the answers

What is the key difference between inertial mass and gravitational mass?

<p>Inertial mass determines resistance to acceleration, while gravitational mass determines the strength of gravitational interaction. (A)</p> Signup and view all the answers

In the context of circular motion, what direction does the centripetal acceleration vector $\vec{a}_c$ point?

<p>Toward the center of the circle. (A)</p> Signup and view all the answers

What does the equivalence principle suggest regarding inertial and gravitational mass?

<p>Inertial mass is experimentally equal to gravitational mass. (A)</p> Signup and view all the answers

In the formula for centripetal acceleration $\vec{a}_c = -\frac{v^2}{r} \hat{r}$, what does $\hat{r}$ represent?

<p>A unit vector pointing toward the center of the circle. (C)</p> Signup and view all the answers

What is the relationship between the work done by external forces and the kinetic energy of an object, as described by the Work-Kinetic Energy Theorem?

<p>The work done is equal to the change in kinetic energy. (D)</p> Signup and view all the answers

Under what condition is the total linear momentum of a system of point-like objects conserved?

<p>When no external forces act on the system. (C)</p> Signup and view all the answers

A planet orbits the Sun in an elliptical path. According to Kepler's laws, what quantity remains constant during the orbit?

<p>The rate at which a line connecting the planet to the Sun sweeps out area. (B)</p> Signup and view all the answers

What does the Center-of-Mass Theorem state regarding the motion of the center of mass of a solid body?

<p>It is determined by the net external force acting on the system. (C)</p> Signup and view all the answers

How does the moment of inertia affect the speed of rolling cylinders on a slope?

<p>Cylinders with smaller moment of inertia roll faster. (D)</p> Signup and view all the answers

What is the direction of electric field lines in relation to positive and negative charges?

<p>Field lines point away from positive charges and toward negative charges. (A)</p> Signup and view all the answers

What is the relationship between electric potential energy ($U_e$), charge ($q$), and electric potential ($V$)?

<p>$U_e = qV$ (B)</p> Signup and view all the answers

According to Ohm's Law, how are voltage ($V$), current ($I$), and resistance ($R$) related in a conductor?

<p>$V = IR$ (C)</p> Signup and view all the answers

How is the magnitude of the magnetic field ($B$) around a straight, current-carrying wire related to the distance ($r$) from the wire?

<p>$B$ is inversely proportional to $r$. (C)</p> Signup and view all the answers

A lab experiment involves a mass on a string rotating in a horizontal circle. Which force is responsible for maintaining this circular motion?

<p>Centripetal force (C)</p> Signup and view all the answers

Imagine lifting an object to a certain height. What best describes work done by gravity in this scenario, independent of the path taken?

<p>The work is negative and equal to the change in gravitational potential energy. (A)</p> Signup and view all the answers

Which of the following best explains the relationship between net torque ($\vec{\tau}$), the moment of inertia ($I$), and angular acceleration ($\vec{\alpha}$) for a macroscopic solid body?

<p>$\vec{\tau} = I \vec{\alpha}$ (D)</p> Signup and view all the answers

What does the theorem on angular momentum describe for a rotating solid body?

<p>$\vec{L} = I \vec{\omega}$ (A)</p> Signup and view all the answers

If a current loop is placed in a magnetic field, what determines the torque on the loop?

<p>The loop's area, the current flowing through it, and external magnetic field. (C)</p> Signup and view all the answers

How is the square of the orbital period ($T$) related to the semi-major axis ($a$) in Kepler's Third Law?

<p>$T^2 / a^3 = \text{constant}$ (C)</p> Signup and view all the answers

Flashcards

Solenoid Magnetic Field

Inside a solenoid, the magnetic field is uniform and given by B=μ₀nI, where n is turns per unit length.

Force on a Current-Carrying Wire

The force on a current-carrying wire in a magnetic field is F=IL×B, where L is the length vector of the wire.

Force on a Moving Charge

The force on a charge q moving with velocity v in a magnetic field B is F=qv×B.

Faraday's Law of Induction

A changing magnetic field induces an electric field, described by E=−dΦB/dt, where ΦB is the magnetic flux.

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Resistor vs Capacitor vs Solenoid Response

For alternating voltage: Resistor current and voltage are in phase; Capacitor current leads voltage by 90°; Solenoid current lags voltage by 90°.

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Angular Velocity (ω⃗)

A vector indicating the axis and rate of rotation of an object.

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Linear Velocity (v⃗)

The velocity of a point-like object, given by v⃗ = ω⃗ × r⃗.

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Newton's First Law of Motion

An object stays at rest or moves uniformly unless acted upon by a net external force.

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Newton's Second Law of Motion

The net force F⃗ equals mass m times acceleration a⃗: F⃗ = m a⃗.

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Inertial Mass (m_inertial)

Measures an object's resistance to acceleration when a force is applied.

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Gravitational Mass (m_grav)

Determines the strength of the gravitational force on an object.

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Centripetal Acceleration (a⃗_c)

Acceleration directed towards the center of a circular path: a⃗_c = −(v^2/r) r̂.

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Position Vector (r⃗)

A vector describing an object's position relative to a reference point.

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Centripetal Force

The force required to maintain circular motion, equal to m (v²/r).

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Work-Kinetic Energy Theorem

The work done by external forces equals the change in kinetic energy (W = ΔK).

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Friction's Effect on Work

Work done by friction is negative, reducing kinetic energy.

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Conservation of Linear Momentum

Total linear momentum of a system is conserved if no external forces act (P = Σ(m_i * v_i)).

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Gravitational Force Formula

The force between two masses is F_g = G (m1 * m2)/r².

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Kepler’s First Law

Planets orbit the Sun in elliptical paths.

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Gravitational Potential Energy

Energy associated with an object's position in a field; U_g = mgh.

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Newton's Second Law (Solid Body)

Net force equals mass times acceleration (F = m a_cm).

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Angular Momentum Formula

The angular momentum of a rotating body is L = Iω.

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Work on Rotating Bodies

Work equals change in rotational kinetic energy (W = ΔK_rot).

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Electric Force Between Charges

The electric force is F_e = k(q1 * q2)/r².

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Electric Field Definition

The electric field is the force per unit charge (E = F_e/q).

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Electric Potential Energy Equation

The electric potential energy is U_e = qV, where V is the voltage.

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Ohm's Law

The current through a conductor is proportional to voltage (V = IR).

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Magnetic Field Around Wire

The magnetic field near a straight wire is B = (μ₀ I)/(2π r).

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Study Notes

Rotation of a Point-Like Object

  • Angular velocity (ω) is a vector along the axis of rotation, following the right-hand rule.
  • Linear velocity (v) is calculated as the cross product of angular velocity (ω) and position vector (r): v = ω × r

General Motion

  • One-dimensional motion uses position (x(t)), velocity (v(t) = dx/dt), and acceleration (a(t) = dv/dt).
  • Multi-dimensional motion uses position vector (r(t)), velocity vector (v(t) = dr/dt), and acceleration vector (a(t) = dv/dt).

Newton’s Laws for a Point-Like Object

  • First Law (Inertia): An object remains at rest or in uniform motion unless acted upon by an external force.
  • Second Law: Acceleration (a) is proportional to net force (F) and inversely proportional to mass (m): F = ma
  • Difference: If net force (F) is zero, the first law describes constant velocity, and the second law gives zero acceleration, consistent with the first law.
  • Inertial vs. Gravitational Mass:
    • Inertial mass (minertial) represents resistance to acceleration (F = minertiala).
    • Gravitational mass (mgrav) determines the strength of gravitational interaction (Fg = mgravg).
    • Experimentally, minertial = mgrav (equivalence principle).

Circular Motion of a Point-Like Object

  • Centripetal acceleration (ac) is given by: ac = -v2/r * rÌ‚, where v is speed, r is radius, and rÌ‚ is the unit vector toward the center.
  • Centripetal force (Fc) is needed for circular motion: Fc = mac = -mv2/r * rÌ‚

Work-Kinetic Energy Theorem

  • Work (W) done by external forces equals the change in kinetic energy (ΔK): W = ΔK = Kf - Ki
  • Friction reduces kinetic energy; work done by friction is negative.
  • Uniform rotation has zero work due to constant speed and kinetic energy.

Theorem on Linear Momentum for a System of Point-Like Objects

  • Total linear momentum (P) is conserved if no external forces act on a system: P = Σi mivi

Gravitational Force and Kepler’s Laws

  • Gravitational force (Fg) between two masses (m1, m2) separated by distance (r) is: Fg = Gm1m2/r2
  • Kepler's Laws:
    • Planets orbit the Sun in elliptical paths.
    • A line connecting a planet to the Sun sweeps out equal areas in equal times.
    • T2/a3 = constant, where T is orbital period and a is semi-major axis.

Gravitational Potential Energy

  • Gravitational potential energy (Ug) is energy related to an object's position in a gravitational field: Ug = mgh (for small heights near Earth's surface).
  • Work done by gravity when lifting an object is the negative change in gravitational potential energy: W = -ΔUg
  • For planetary motion, Ug = -GMm/r (where M is the Sun's mass, and r is the distance from the Sun).

Newton’s Laws for a Macroscopic Solid Body

  • Linear motion: Net force (F) on a solid body equals its mass (m) times the acceleration (a) of its center of mass: F = macm
  • Rotation: Net torque (Ï„) equals the moment of inertia (I) times the angular acceleration (α): Ï„ = Iα
  • Center-of-mass theorem: Center-of-mass motion is determined by net external force.

Theorem on Angular Momentum for Rotation of Solid Bodies

  • Angular momentum (L) of a rotating solid body is: L = Iω, where I is the moment of inertia and ω is angular velocity.

Work-Kinetic Energy Theorem for Rotation

  • Work (W) done by external torques equals the change in rotational kinetic energy: W = ΔKrot = (1/2)Iωf2 - (1/2)Iωi2.
  • Rolling cylinders with smaller moments of inertia roll faster down a slope.

Electric Force Between Two Charged Objects

  • Electric force (Fe) between two charges (q1, q2) separated by distance (r) is: Fe = kq1q2/r2 * rÌ‚, where k = 1/(4πε0).

Electric Field and Field Lines

  • Electric field (E) is force per unit charge: E = Fe/q
  • Field lines point away from positive charges and toward negative charges.
  • Torque (Ï„) on a dipole in an external field (E) is: Ï„ = p × E, where p is the dipole moment.

Electric Potential Energy, Potential, and Voltage

  • Electric potential energy (Ue) of a charge (q) in an electric field is: Ue = qV, where V is the electric potential.
  • Voltage is work done per unit charge to move a charge in an electric field.

Electric Current, Voltage, and Ohm’s Law

  • Electric current (I) is the flow of charge per unit time: I = Δq/Δt
  • Ohm's Law: Current (I) through a conductor is proportional to the voltage (V): V = IR, where R is resistance.

Dipole Moment of a Current Loop

  • Magnetic dipole moment (μ) of a current loop is: μ = IA, where I is current and A is the area vector of the loop.
  • Torque (Ï„) on a dipole in a magnetic field (B) is: Ï„ = μ × B

Magnetic Field Near Current-Carrying Wires

  • Straight wire: Magnetic field (B) around a straight wire is: B = μ0I/(2Ï€r).
  • Solenoid: Inside a solenoid, magnetic field (B) is uniform: B = μ0nI, where n is the number of turns per unit length.

Forces on a Current-Carrying Wire and Moving Charge

  • Force on a wire (F) in a magnetic field (B) is: F = IL × B, where L is the length vector of the wire.
  • Force on a charge (q) moving with velocity (v) in a magnetic field (B) is: F = qv × B

Electric Induction

  • Changing magnetic field induces an electric field (Faraday's law): E = -dΦB/dt, where ΦB is magnetic flux.

Response of Electric Elements to Alternating Voltage

  • Resistor: Current and voltage are in phase.
  • Capacitor: Current leads voltage by 90°.
  • Inductor: Current lags voltage by 90°.

Electromagnetic Waves and Light

  • Electromagnetic waves are oscillating electric and magnetic fields propagating at the speed of light (c).
  • Light exhibits interference (Young's double-slit experiment).

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