sy15_oct24_07hc - Page 1 Physics 207 – Lecture 15 Physics...

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Unformatted text preview: Page 1 Physics 207 – Lecture 15 Physics 207: Lecture 15, Pg 1 Physics 207, Physics 207, Lecture 15, Oct. 24 Lecture 15, Oct. 24 Agenda: Chapter 11, Finish, Chapter 13, Just Start Agenda: Chapter 11, Finish, Chapter 13, Just Start Assignment: For Monday read Chapter 13 carefully (you may Assignment: For Monday read Chapter 13 carefully (you may skip the parallel axis theorem and vector cross products) skip the parallel axis theorem and vector cross products) c MP Homework 7, Ch. 11, 5 problems, available today, MP Homework 7, Ch. 11, 5 problems, available today, Due Wednesday at 4 PM Due Wednesday at 4 PM c MP Homework 6, Due tonight MP Homework 6, Due tonight c Chapter 11: x Variable forces x Conservative vs. Non-conservative forces x Power x Work & Potential Energy • Start Chapter 13 x Rotation x Torque Physics 207: Lecture 15, Pg 2 Lecture 15, Lecture 15, Exercise 1 Exercise 1 Work in the presence of friction and non Work in the presence of friction and non-contact forces contact forces A. 2 B. 3 C. 4 c A box is pulled up a rough ( μ > 0) incline by a rope-pulley- weight arrangement as shown below. x How many forces are doing work on the box ? x Of these which are positive and which are negative? x Use a Force Body Diagram x Compare force and path v Physics 207: Lecture 15, Pg 3 Lecture 15, Lecture 15, Exercise 1 Exercise 1 Work in the presence of friction and non Work in the presence of friction and non-contact forces contact forces c A box is pulled up a rough ( μ > 0) incline by a rope-pulley-weight arrangement as shown below. x How many forces are doing work on the box ? x And which are positive and which are negative? x Use a Force Body Diagram (A) (A) 2 (B) (B) 3 is correct (C) (C) 4 v f mg N T Physics 207: Lecture 15, Pg 4 Work and Varying Forces (1D) Work and Varying Forces (1D) c Consider a varying force F(x) F x x ∆ x Area = F x ∆ x F is increasing Here W = F · ∆ r becomes dW = F dx F θ = 0° Start Finish Work is a scalar, the rub is that there is no time/position info on hand ∫ = f i x x dx x F W ) ( F ∆ x Physics 207: Lecture 15, Pg 5 ∆ x v o m t o F Example: Example: Work Kinetic Work Kinetic-Energy Theorem Energy Theorem • How much will the spring compress (i.e. ∆ x ) to bring the object to a stop (i.e., v = 0 ) if the object is moving initially at a constant velocity (v o ) on frictionless surface as shown below ? spring compressed spring at an equilibrium position V=0 t m Notice that the spring force is opposite to the displacement. For the mass m, work is negative For the spring , work is positive Physics 207: Lecture 15, Pg 6 Example: Example: Work Kinetic Work Kinetic-Energy Theorem Energy Theorem • How much will the spring compress (i.e. ∆ x x = = x f- x i ) to bring the object to a stop (i.e., v = 0 ) if the object is moving initially at a constant velocity (v o ) on frictionless surface as shown below ?...
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This note was uploaded on 10/30/2011 for the course PHYS 207 taught by Professor Winnokur during the Spring '06 term at University of Wisconsin.

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sy15_oct24_07hc - Page 1 Physics 207 – Lecture 15 Physics...

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