2D Particle Motion: Coordinate Systems

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Questions and Answers

In two-dimensional motion analysis, which type of coordinate system is characterized by radial distance and angle?

  • Tangential coordinates
  • Polar coordinates (correct)
  • Central paths
  • Cartesian coordinates

Which of the following coordinate systems involves describing the motion of a particle along a curved path using coordinates that are tangent and normal to the path?

  • Polar coordinates
  • Cartesian coordinates
  • Central paths
  • Tangential coordinates (correct)

If the acceleration of a particle is given as a function of time, what mathematical operation is used to determine the velocity of the particle?

  • Differentiation
  • Vector cross product
  • Integration (correct)
  • Laplace transform

Given a particle moving in a plane with acceleration (\vec{f} = 3t \hat{i} + 2 \hat{j}), which expression represents its velocity (\vec{v}) if the initial velocity at $t=0$ is (\vec{v_0} = 3\hat{i} - 2\hat{j})?

<p>(\vec{v} = (1.5t^2 + 3)\hat{i} + (2t - 2)\hat{j}) (C)</p>
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A particle's motion is described in Cartesian coordinates with its position vector given by (\vec{r} = x\hat{i} + y\hat{j}). If (\hat{i}) and (\hat{j}) are unit vectors along the x and y axes, respectively, what do 'x' and 'y' represent?

<p>Displacement components (D)</p>
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Given the velocity components of a particle as functions of time, what mathematical operation determines the displacement of the particle?

<p>Integration (C)</p>
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A particle starts from position ((3, -2)) with an initial velocity of (3\hat{i} - 2\hat{j}) and is subjected to a constant acceleration of (3\hat{i} + 2\hat{j}). What is the position vector (\vec{r}) of the particle at time (t)?

<p>(\vec{r} = (1.5t^2 + 3t + 3)\hat{i} + (t^2 - 2t - 2)\hat{j}) (A)</p>
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What are the unit vectors in the directions of increasing (r) and (\theta) in a polar coordinate system?

<p>(\hat{r}) and (\hat{\theta}) (A)</p>
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Given (\hat{r} = \cos \theta \hat{i} + \sin \theta \hat{j}) and (\hat{\theta} = -\sin \theta \hat{i} + \cos \theta \hat{j}), what is the time derivative of (\hat{r}), denoted as (\dot{\hat{r}})?

<p>(\dot{\hat{r}} = \dot{\theta} \hat{\theta}) (B)</p>
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In polar coordinates, if the position vector is given by (\vec{r} = r \hat{r}), what is the expression for the velocity vector (\vec{v})?

<p>(\vec{v} = \dot{r} \hat{r} + r \dot{\theta} \hat{\theta}) (A)</p>
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What are the radial and transverse components of acceleration in polar coordinates?

<p>((\ddot{r} - r\dot{\theta}^2)) and ((r\ddot{\theta} + 2\dot{r}\dot{\theta})) (D)</p>
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In central force motion, what quantity is conserved?

<p>Angular momentum (C)</p>
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If a particle moves in a plane such that its speed components are constant, and one component is along a fixed line OX, while the other is perpendicular to OP (where O is the origin and P is the particle's position), what can be said about the force acting on the particle?

<p>It is inversely proportional to the distance from O (D)</p>
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A particle is moving under a central force F, and its motion is described by the equations (m(\ddot{r} - r\dot{\theta}^2) = -F) and (\frac{d}{dt}(r^2\dot{\theta}) = 0). What does the second equation imply?

<p>The angular momentum is conserved. (B)</p>
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What is the differential equation that describes the path of a particle under a central force, where (u = 1/r)?

<p>(\frac{d^2u}{d\theta^2} + u = \frac{F}{h^2u^2}) (D)</p>
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What physical quantity does the constant (h) represent in the analysis of central force motion, and how is it related to the particle's motion?

<p>Angular momentum per unit mass; remains constant during motion. (D)</p>
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What condition defines an apsidal point in a central force orbit?

<p>The radial velocity is zero. (C)</p>
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What is the term for the angle between two consecutive apsidal points in a central force orbit?

<p>Apsidal angle (D)</p>
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If a particle moves under a central force that results in a circular orbit, what can be said about the speed of the particle?

<p>It is constant. (B)</p>
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A particle is projected from an apsidal distance (a) with a speed equal to (\sqrt{2}) times the speed for a circular orbit of radius (a). What is the equation of the path?

<p>(r = a \cos \theta) (B)</p>
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What general equation relates the force to u in a central orbit?

<p>(\frac{d^2u}{d\theta^2} + u = \frac{\mu}{h^2 u^2}) (C)</p>
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What shape of orbit would one expect if (n = 1)?

<p>circle (D)</p>
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What formula is used to describe the tangent made as the distance between a curve and a vector nears zero?

<p>(tany = lim_{\Delta r \to 0} r\frac{\Delta \theta}{\Delta r}) (A)</p>
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In what direction would there be zero traverse acceleration?

<p>in the direction of the central pole. (A)</p>
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What is the simplified APSE distance equation?

<p>(M =r) (D)</p>
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What formula would express the relationship between a wire on the horizontal plane to a vertical wire?

<p>((2a^2 + b^2)\frac{\pi}{2 \sqrt{\mu}}) (B)</p>
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If a particle can experience a force (\mu u^3) what equation would one use?

<p>(h=1M = \frac{\mu}{ a \sqrt{2}}\) (C)</p>
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If angular momentum is conserved can it only move in one way?

<p>angularly (A)</p>
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If considering the force on an object, what direction would also need considering?

<p>the equal and opposite direction (D)</p>
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Flashcards

Cartesian Coordinates

A coordinate system using two perpendicular axes (x, y) to define a point's position.

Polar Coordinates

A coordinate system using distance from origin (r) and angle (θ) to define a point's position.

Motion in Cartesian Coordinates

Components of acceleration, velocity and displacement. Found using integration.

Angle φ in Polar Coordinates

Angle between the tangent to the curve and the radial line.

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Apses

Points where the radial distance reaches a maximum or minimum.

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Apsidal Distance

Distance between apse and center, characterizes the orbit's size.

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Central Orbit

An orbit where a particle moves under a central force.

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Apsidal Angle

The turning points of the orbit trajectory.

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Central Force

When a particle is moving along a curve such that force is directed always towards the fixed point.

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h

Equal to the angular momentum, constant in central orbits.

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Study Notes

  • Studying the motion of a particle in two dimensions involves understanding different coordinate systems.
  • Four types of coordinate systems are commonly used: Cartesian, Polar, Central paths, and Tangential coordinates.

Cartesian Coordinates

  • This system uses two perpendicular axes, traditionally labeled ox and oy.
  • A particle's position, denoted as p, can be described at any given moment using these axes.
  • Both acceleration and velocity have components along each axis.
  • The position vector r can be expressed as r = xi + yj, where x and y are the coordinates along the ox and oy axes, respectively, and i and j are unit vectors in the positive direction of each axis.
  • Similarly, velocity v is expressed as v = vxi + vyj, and acceleration f as f = fxi + fyj.
  • If the acceleration f is known, both velocity v and position r can be determined through integration.

Polar Coordinates

  • In this system, the position of a particle P is defined by coordinates (r, θ).
  • Where r is the radial distance from the origin and θ is the angle with respect to the ox axis.
  • i and j represent unit vectors in the directions of ox and oy.
  • Unit vectors rÌ‚ and θ̂ represent the directions of increasing r and θ, respectively.
  • It is clear by figure that rÌ‚ = icosθ + jsinθ and θ̂ = -isinθ+ jcosθ.
  • Taking the derivative of rÌ‚ and θ̂ with respect to time, we get r̂’ = θ’θ̂ and θ̂’ =-θ’rÌ‚.
  • The position vector from the origin to P can be expressed as r = oP = rrÌ‚

Velocity in Polar Coordinates

  • Velocity has two components:
    • ṙ, which indicates the rate of change of radial distance in the direction of increasing r.
    • rθ̇, which represents the tangential velocity component in the direction of increasing θ.

Acceleration in Polar Coordinates

  • The acceleration f in polar coordinates is given by:
    • fr = r̈ - rθ̇2 (radial component)
    • fθ = rθ̈ + 2ṙθ̇ = 1/r d/dt (r2θ̇) (tangential component)
    • The radial component (r̈ - rθ̇2) is also called the radial acceleration.
    • The tangential component rθ̈ + 2ṙθ̇ also is called the transverse acceleration.

Examples of motion in polar Coordinates

  • A particle P moves in a plane such that the components of its velocity are constant, one of the components is along a constant line ox and the other is perpendicular to oP. Find the equation of the particle's path. If a force that always acts in the direction of Po impacts particle P, prove that this force is inversely proportional to the square of the distance between it and 0.
    • assume that are V1 and V2 where V1 is velocity in direction of ox and V2 the other in direction of oQ. Also á¹™ is the component of velocity in increasing direction r.
    • therefore V1 = á¹™cosθ and V2 = rθ̇ + V1sinθ
    • from this by separating the variables ∫dr/r=∫V1cosθ/(V2-V1sinθ)
    • this will lead to the formula r = l/(1-µsinθ), (where l=C/V2 and µ=V1/V2).
    • this (above) is the equation of the particle's path
  • The magnitude of the force that is affecting to that trajectory is F = (mlh^2/r) , (l=(C/V2 or µ/V2) and hl= (µcosθ) -From differential geometry (dr/dt dθ/dt dθ/dr)=(2/r^3)

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