Motion in 2D and 3D

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Questions and Answers

Why must the descriptions of motion be extended to two- and three-dimensional situations?

  • To simplify the calculations of motion.
  • Because all objects move in straight lines.
  • Because objects do not always move in a single line. (correct)
  • To avoid using vector quantities.

What is the definition of the position vector of a particle at an instant?

  • A vector representing the particle's acceleration.
  • A vector tangent to the particle's path.
  • A vector that goes from the origin to the particle's location. (correct)
  • A scalar that indicates the particle's speed.

The average velocity vector always points in the same direction as which of the following?

  • The displacement vector. (correct)
  • The final position vector.
  • The acceleration vector.
  • The initial position vector.

The instantaneous velocity vector is always what to the path of a projectile?

<p>Tangent (D)</p> Signup and view all the answers

What represents the speed of a projectile?

<p>The magnitude of its instantaneous velocity. (D)</p> Signup and view all the answers

What is the relationship between a particle's velocity components and its coordinates?

<p>Velocity components are the time derivatives of the coordinates. (A)</p> Signup and view all the answers

If a particle is moving in the xy-plane, what must be true of z and (v_z)?

<p>Both must be zero. (B)</p> Signup and view all the answers

What does the instantaneous acceleration vector describe?

<p>Changes in both speed and direction of velocity. (B)</p> Signup and view all the answers

If the direction of a car's acceleration is opposite to the acceleration, what will occcur?

<p>The car will slow down. (A)</p> Signup and view all the answers

The velocity vector is always tangent to which of the following?

<p>The trajectory (D)</p> Signup and view all the answers

Which statement is correct concerning instantaneous acceleration and average acceleration?

<p>Instantaneous is the limit of average as the interval approaches zero. (D)</p> Signup and view all the answers

A particle is moving along a curved path. When is the acceleration tangent to this path?

<p>Only if the path is a straight line. (D)</p> Signup and view all the answers

If a particle is moving in a curved path, which direction does the acceleration vector point?

<p>Toward to the inside of the curved path. (C)</p> Signup and view all the answers

Given that (a_{\parallel}) is the component of the acceleration parallel to a particle's velocity and (a_{\perp}) is the component perpendicular to the velocity, what do these components tell us?

<p>(a_{\parallel}) tells changes in speed, (a_{\perp}) tells changes in direction. (D)</p> Signup and view all the answers

When an object is turning, what must be true about its acceleration and velocity?

<p>The velocity needs to be changing, and the acceleration needs to be non-zero. (C)</p> Signup and view all the answers

The equation is given: $y = (tan \alpha_0)x - \frac{g}{2(v_0 cos \alpha_0)^2}x^2$. This refers to which of the following?

<p>The shape of the trajectory. (A)</p> Signup and view all the answers

If you want to achieve the maximum range for a projectile, what launch to you use?

<p>45° (D)</p> Signup and view all the answers

While a projectile is in motion, what statements are true?

<p>The gravity affects the vertical component of velocity. (A)</p> Signup and view all the answers

How you can calculate the projectile coordinate as a function of time?

<p>All of the above (D)</p> Signup and view all the answers

What is the value of ax and ay respectively while the projectile is in flight?

<p>a = 0, and a = -g (C)</p> Signup and view all the answers

At which point is the projectile on a trajectory if the following conditions are satisfied: uy = 0, the particle still exists, still possesses kinetic energy, gravity still exists

<p>The highest Point. (A)</p> Signup and view all the answers

Which best describes uniform circular motion?

<p>Path that has constant speed (D)</p> Signup and view all the answers

An object has a period, denoted T. How is the object's magnitude acceleration related to the radius of the object?

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

Which statement about the difference between circular and projectile motion is correct?

<p>All statements are incorrect (D)</p> Signup and view all the answers

Assuming that an object goes around a loop, which statement is guaranteed to be true?

<p>The speed is fastest when the arad is maximized. (D)</p> Signup and view all the answers

If relative velocity is important, which one of the following needs to be true?

<p>Objects close to each other at extremely high speeds. (C)</p> Signup and view all the answers

Which of the following describes the expression, UP/A-x = UP/B-x + UB/A-x?

<p>It describes the velocity along a line. (A)</p> Signup and view all the answers

Why does the statement below need to be solved to derive an efficient problem setup? 'The known u(T/E) is an actual and rearranges: UT/E-x = UT/Y-x + UY/E-x'

<p>To solve UT/Y-x, by expressing. (C)</p> Signup and view all the answers

If A and B frame of reference, then which of the following statements is true?

<p>UA/B= −UB/A. (C)</p> Signup and view all the answers

If you are told to solve for 2 unknowns during an equation, but it requires 3 dimensions, what can you do?

<p>Pay close attention to the subsripts then solve the equation. (C)</p> Signup and view all the answers

In projectile motion, what is the purpose of setting (y = 0)?

<p>This satisfies for when the ball lands at ground. (D)</p> Signup and view all the answers

A tranquilizer dart having relatively low muzzle velocity reaches point P before touching the monkey. In this case assuming drag has been accounted for, what location will the monkey be?

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

A and B refer to which of the following?

<p>A is for the stationary, B is for moving. (D)</p> Signup and view all the answers

What is the Galilean transformation?

<p>Equation of relative velocity. (B)</p> Signup and view all the answers

At high speeds near c, what is the value of calculating the Galilean relativity with the train and speed, assuming the train moves at c to the same direction?

<p>Speeds get very small (A)</p> Signup and view all the answers

If a plane goes to 20 degrees west of north at what point would it be heading?

<p>Direction the plane is blowing towards. (B)</p> Signup and view all the answers

If the value airspeed indicator is 100km per second at -30 degrees from the starting point. Which statement is correct?

<p>Value gives speed and direction for earth. (B)</p> Signup and view all the answers

When solving for the magnitude and or the direction of a vector, which of the following is true?

<p>Requires equations to be solved. (D)</p> Signup and view all the answers

An artillery shell is fired, and one wishes to maximize the range with the same shell. If the same cannon is fired on that same shell underwater at 1000 atm of pressure, the range the shell travels is best described by which one of the following statements (assume cannon survives)?

<p>Decreases, because there is drag that affects the result (A)</p> Signup and view all the answers

Flashcards

Position Vector

Vector that goes from the origin to the particle's location.

Average Velocity (vav)

Displacement divided by the time interval.

Instantaneous Velocity (v)

Instantaneous rate of change of position with time; vector.

Velocity

Speed and direction.

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Instantaneous Acceleration (a)

Time derivative of the velocity vector; describes changes in speed and direction.

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Parallel Acceleration (a||)

Component of acceleration parallel to path (tangent) and affects the speed.

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Perpendicular Acceleration (a┴)

Component of acceleration perpendicular to path (normal) and affects direction.

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Projectile

An object given initial velocity and affected by gravity and air resistance.

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Trajectory

Path followed by a projectile.

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Projectile Motion

Combination of horizontal motion with constant velocity & vertical motion with constant acceleration.

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Horizontal Distance

Horizontal range (R)

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Uniform Circular Motion

Motion in a circle at constant speed.

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Radial Acceleration (arad)

Acceleration is inward.

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Nonuniform Circular Motion

Motion in a circle with varying speed.

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Tangential Component(atan)

Extra acceleration in nonuniform circular motion (dv/dt)

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Relative velocity

Velocity relative to a particular observer.

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Frame of Reference

Coordinate system plus a time scale.

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Study Notes

  • Chapter 3 discusses motion in two or three dimensions, extending concepts from one-dimensional motion analysis.
  • Includes describing motion with vector quantities like displacement, velocity, and acceleration in 2D and 3D space.

Position and Velocity Vectors

  • The position vector pinpoints a particle's location in space relative to the coordinate system's origin.
  • Represented as ŕ = xî + yĵ + zk, using Cartesian coordinates, where x, y, and z are vector components.
  • Displacement is the change in position (∆ř) and is calculated as ∆ř = ř₂ - ř₁.
  • Average velocity ( vav) is displacement over a time interval: vav = ∆ř / ∆t.
  • Instantaneous velocity (v) is the limit of average velocity as the time interval approaches zero, v = lim(∆t→0) ∆ř / ∆t = dŕ/dt.

Vector Facts

  • Instantaneous velocity direction is tangent to the particle’s path.
  • Components of instantaneous velocity are the time derivatives of the coordinates: vx = dx/dt, vy = dy/dt, vz = dz/dt.
  • Magnitude of instantaneous velocity (speed) is calculated using the Pythagorean theorem: v = √(vx² + vy² + vz²).

Acceleration Vector

  • Acceleration describes changes in velocity, including both speed and direction.
  • Average acceleration (av) is the change in velocity over a time interval: aav = ∆v / ∆t.
  • Instantaneous acceleration (a) is the limit of the average acceleration as the time interval approaches zero: a = lim(∆t→0) ∆v / ∆t = dv/dt.
  • Direction need not be tangent to the path. Points toward the concave side for curved paths.
  • Components are the time derivatives of velocity components: ax = dvx/dt, ay = dvy/dt, az = dvz/dt or can be expressed, ax = d²x/dt², ay = d²y/dt², az = d²z/dt².
  • Acceleration can be divided into components parallel (a||) and perpendicular (a┴) to the path. a|| affects speed and a┴ affects direction.

Projectile Motion

  • Projectile motion involves objects launched into the air, affected by gravity and, in simplified models, neglecting air resistance.
  • Trajectory lies in a vertical plane that is determined by the initial velocity vector.
  • Treat horizontal and vertical motions separately.
  • Horizontal motion has constant velocity (ax = 0), U x = Vox , x = xo + Voxt.
  • Vertical motion has constant acceleration (ay= -g), Uy = Uoy, y = yo + Uoyt - gt2.
  • Equations (3.19) to (3.22) describe position and velocity at any time t, assuming initial position as the origin.
  • Trajectory shape in projectile motion can be expressed y = (tanα₀)x - (g / 2(vo cosα₀)²)x² which is a parabolic path.

More facts about projectile motion

  • Maximum height reached is when vertical velocity component equals zero.
  • Horizontal range (R) is greatest at a launch angle of 45 degrees = (vo² sin 2α₀) / g - (only when the launch and landing are equal).

Uniform Circular Motion

  • Uniform circular motion occurs. A particle moves with constant speed in a circle.
  • Acceleration is always directed toward the circle's center with magnitude: arad = v²/R. Radial is toward the center.
  • Acceleration rewritten in terms of period (T): arad = 4π²R / T².
  • Tangential acceleration (a) is zero since speed is constant.

Nonuniform circular motions

  • Nonuniform circular motion occurs when speed changes
  • Radial component is still arad = v²/R
  • Tangential component atan = dv/dt and affects change in speed

Relative Motion

  • Describes how motion appears to different observers in different reference frames.
  • UP/A is P's velocity relative to frame A, *UP/B.
  • Transformation equation: UP/A = UP/B + UB/A.
  • Relative velocity equation relies on vector addition.

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