Cuesta College :: Physics 205A :: Fall 2017
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"She had felt a collision with him and known that she had wanted this her whole life: to crash for just one moment into another person at such a velocity as to fuse with him."
     --Ali Shaw, The Girl With Glass Feet, Picador (2011), p. 272.

Quiz 4 worksheet questions (*.pdf)

Ch. 7.2: Conservation of Momentum
Ch. 7.3: Collisions in One Dimension (*.blog)
     Collision flowchart (*.gif)
     Ex: coupled freight car and locomotive (*.blog)
     Ex: kinetic energy loss of completely inelastic collision (*.blog)
     Ex: categorizing a cart collision (*.blog)

Read Physics, 10/e, Chs. 9.1, 9.2
Preview online presentation (*.blog), (*.blog)
     ("Torque" (Greek letter τ) measures the "twistiness" of a force, and has both direction and magnitude.  The ± direction depends on whether it would cause a ccw or cw rotation.  The magnitude depends on the magnitude of the force, and the "perpendicular lever arm" ℓ.  If ℓ is not perpendicular to the force, a right triangle must be drawn where the force "line of action" and the perpendicular lever arm are the legs of the triangle.  Using ℓ to calculate torque is somewhat esoteric, but other  methods to calculate torque (perpendicular force components, cross-products, tensors) are even more peculiar.)

Physics quiz question: pellet bouncing off of block (*.blog)
Physics quiz question: Cadillac ATS and BMW 328i collision (*.blog)
Physics quiz question: Mission Impossible: II mid-air collision, conservation laws (*.blog)
Physics quiz question: Mission Impossible: II mid-air collision, initial velocity (*.blog)
Physics quiz question: submarine torpedo-eject recoil (*.blog)
Physics midterm problem: categorizing a cart collision (*.blog)
Ch. 7 Problems 23(a), 29(a)
     (assume all velocities directed along ±x-axis)

Due 12:00 AM before start of next lecture
     Reading assignment 16 (*.html)
     Homework report 16 (*.html)
     "Keep-Quit-Start" Survey (*.html) (extra-credit)

"Get a perfectly symmetrical plank, and balance it across a sawhorse. Place the hawg on one end of the plank, and pile rocks on the other end until it has just returned to its equilibrium position. Then guess the weight of the rocks."
     --Attributed to Robert Burns, as reported by Robert E. Machal, 
       "Principles of Operations Research: The Burns Balance," Interfaces, 
       Institute of Management Sciences (November 1975), vol. 5, p. 63.
Quiz 5 worksheet questions (*.pdf)

Chs. 9.1, 9.2: Torque, Rigid Objects in Equilibrium (*.blog)
     Ex: diagonally-propped beam (*.blog)
Quiz 4 announcements
     Monday, 10/30, 11:00-11:25 AM
     Closed-book, closed-notes
     Ten multiple-choice questions
          Work (_____ questions)
          Energy types, conservation (_____ questions)
          Impulse, momentum (_____ questions)
          Collisions (_____ questions)
     No work needs to be shown; no partial credit
     No Scantrons; circle answers directly on quiz
     Bring your scientific calculator

Check Twitter announcements: #CuestaPhys205A
Read Physics, 10/e, Chs. 8.2 (angular velocity), 8.6, 9.4 (moment of inertia), 9.5
Preview online presentation (*.blog) 
     (Recognize changes (increases/decreases) in rotational kinetic energy, and how rotational speed ω is related to translational speed v for objects that roll without slipping.  The "moment of inertia" is a configuration-dependent factor of how mass is arranged around a rotation axis, and this term is included in the calculation of rotational kinetic energy.  Then in the ideal case that there is no external work done, energy is "conserved" and can transfer between different forms of kinetic energy (rotational and translational) and/or potential energy (gravitational and elastic) without loss.)

Physics quiz question: tipping a square plate (*.blog)
Physics quiz question: cable-supported beam (*.blog)
Physics quiz question: torque exerted by post on table (*.blog)
Physics quiz question: tilted Murphy bed (*.blog)
Ch. 9, Examples 1 (p. 219), 2 (p. 220), 3 (pp. 221-222)

Due 12:00 AM before start of next lecture
     Reading assignment 17 (*.html)
     Homework report 17 (*.html)