HTWClass9F07

HTWClass9F07 - Schedule Monday 9/10 HW 2 due Tuesday...

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Unformatted text preview: Schedule Monday 9/10 HW 2 due Tuesday Wednesday 9/12 Pretest 3 due Pretest 4 posted Tuesday Wednesday 9/19 Pretest 4 due Pretest 5 posted Tuesday Wednesday 9/26 Pretest 5 due Thursday Thursday Thursday Friday 9/13 Monday 9/17 HW 3 due HE 1 due HW 4 posted Monday 9/24 HW 4 due Friday 9/21 Friday 9/28 HW 5 posted Physics 100 Fall 2007 First Hour Exam: Monday 10/1 The exam will be taken exclusively from the following cases. Chapter 1: 1, 2 , 3, 4, 5, 7, 10, 11, 12 Chapter 2: 2, 3, 4, 8, 9, 10 Chapter 3: 1, 3, 7, 9, 10, 11 Find these on the web at publisher's site via an `External Link' on Blackboard Physics 100 Fall 2007 HW and Test Problems From HW1 Ch. 1, Pr. 3: On Mars, the acceleration due to gravity is 3.71 m/ s2. What would the rock's velocity be 3 seconds after you dropped it on Mars? v = v0 + a t Velocity at t = starting velocity + acceleration time (t) v = 0 + (3.71 m/s2) 3 s v = (3 3.71) m/s2 s v = 11.13 m/s Explanation: This is the equation to use for constant acceleration. The rock starts from rest so v0 is zero. We then solve for velocity to get the answer. We choose down being positive, but if we choose up being positive, then a = -3.71 m/s2 and the answer is negative, i.e. v = -11.13 m/s. Physics 100 Fall 2007 From HW 2 Chapter 1, Case 1. You're riding on a playground swing. You're traveling back and forth once every few seconds. The diagram shows snapshots of the swing at a sequence of times in its motion. a. At what point(s) in your motion is your velocity zero? Your velocity a b c d e is zero at the top of the swing, pts a and e. At these places, the motion turns around, and therefore, the velocity must be zero in the middle of the turn around. b. At what point(s) in your motion is your gravitational potential energy at its maximum? The gravitational potential energy is mgh, and therefore it is greatest when h, the height is greatest. This occurs at the top of the motion at a and at e. c. At what point(s) in your motion is your kinetic energy at its maximum? The total energy (GPE+KE) must be constant, and so the energy goes back and forth between the gravitational potential energy and the kinetic energy. Since GPE=mgh, when the height is the lowest, GPE is the lowest, so the kinetic energy is greatest, so is the velocity. This occurs at point c. a. ... Physics 100 Fall 2007 Clickers with ID listed below need to be registered - #1774335 #18FC749 #19025B4 K3 H5 Q3 Physics 100 Fall 2007 Observations about Seesaws A balanced seesaw rocks back and forth easily Equal-weight children balance a seesaw Unequal-weight children don't normally balance Moving heavier child inward restores balance Sitting closer to the pivot speeds up the motion Physics 100 Fall 2007 Questions about Seesaws 1. How can we describe its motion? 2. What is the rotational "influence"? 3. Where are Newton's Laws? Physics 100 Fall 2007 Torque Pivot point Physics 100 Fall 2007 Translation and Rotation Variables Translation: Position x Rotation: Angle Velocity v Angular Velocity Translation Newton 1: Inertia Newton 2: m = mass F = force F=ma Physics 100 Fall 2007 Acceleration a Angular Acceleration Rotation I = moment of inertia = torque m I ? == Newton's Law for Rotation Newton's 2nd law (for rotation): Determine direction of torque right hand direction r r = I r is a vector has direction Physics 100 Fall 2007 Calculating Torque Torque L = lever arm = FL How do we determine L? Step 1: Draw line through force Step 2: draw parallel line through pivot L Step 3: L = shortest distance between two lines Physics 100 Fall 2007 Calculating Torque Torque L = lever arm = FL How do we determine L? Step 1: Draw line through force Step 2: draw parallel line through pivot L Step 3: L = shortest distance between two lines Physics 100 Fall 2007 Angular Motion Angular velocity vector : Points along rotation axis Points in "right hand" direction Longer arrow = faster spin Angular acceleration vector Spinning getting faster: in same direction as Spinning slowing: in opposite direction from Physics 100 Fall 2007 for decreasing Moment of Inertia - I I = m r2 m r m r r m I = 2m r2 Physics 100 Fall 2007 Newton's Laws: Translation Newton 1 for linear motion: An object at rest will remain at rest and an object in motion will remain in motion if no force acts on it Newton 2 for linear motion: The force on an object equals the product of the mass times the acceleration. Physics 100 Fall Newton 3 for linear motion: 2007 Newton's Laws: Rotation Newton 1 for rotational motion: An object at rest will remain at rest and an object in motion will remain in motion if no torque acts on it Newton 2 for rotational motion: The torque on an object equals the product of the moment of inertia times the angular acceleration. Newton 3 for rotational motion: Physics 100 Fall 2007 If one object exerts a torque on the second, the second Where to put the screw - Equating torques Book screw s F s =FL L =FL L F Pivot Point Physics 100 Fall 2007 ...
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This note was uploaded on 03/26/2008 for the course PHYS 100 taught by Professor Tsui during the Fall '07 term at UNC.

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