Lecture15

Lecture15 - PHYSICS 149: Lecture 15 Chapter 6: Conservation...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
PHYSICS 149: Lecture 15 • Chapter 6: Conservation of Energy – 6.3 Kinetic Energy – 6.4 Gravitational Potential Energy Lecture 15 Purdue University, Physics 149 1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
ILQ 1 Mimas orbits Saturn at a distance D. Enceladus rbits Saturn at a distance 4D What is the ratio of orbits Saturn at a distance 4D. What is the ratio of the periods of their orbits? A) T m /T e = 1/8 ) T 1 /4 23 2 3 T r B) T m /T e = 1/4 C) T m /T e = 1/2 ) T 2 4 11 m E m T D TD T ⎛⎞ = ⎜⎟⎜⎟ ⎝⎠ = D) T m /T e = 2 64 8 E T ⎜⎟ Lecture 15 Purdue University, Physics 149 2
Background image of page 2
ILQ 2 A pendulum bob swings back and forth along a circular path. Does the tension in the string do any work on the bob? Does gravity do work on the bob? A) only tension does work ) both do work B) both do work C) neither do work D) only gravity does work Lecture 15 Purdue University, Physics 149 3
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Energy • Energy is “conserved” meaning it can not be created nor destroyed – Can change form – Can be transferred otal Energy of an isolated system does not change with Total Energy of an isolated system does not change with time orms Forms – Kinetic Energy Motion – Potential Energy Stored eat – Heat – Mass (E=mc 2 ) nits: oules = kg m 2 s 2 Lecture 15 Purdue University, Physics 149 4 Units: Joules kg m / s
Background image of page 4
Definition of “Work” in Physics • Work is a scalar quantity ( not a vector quantity). • Units: J (Joule), N m, kg m 2 /s 2 , etc. . nit conversion: 1 J =1N =1kg 2 2 Unit conversion: 1 J 1 N m 1 kg m /s • Work is denoted by W (not to be confused by weight W ) . Lecture 15 Purdue University, Physics 149 5
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Total Work hen several forces act on an object the “total” • When several forces act on an object, the total work is the sum of the work done by each force dividually: individually: Lecture 15 Purdue University, Physics 149 6
Background image of page 6
ILQ 1 You are towing a car up a hill with constant velocity . The work done on the car by the normal force is: ) positive A) positive B) negative C) zero F N V T W Normal force is perpendicular to direction of displacement, so work is zero. Lecture 15 Purdue University, Physics 149 7
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
ILQ 2 You are towing a car up a hill with constant velocity . The work done on the car by the gravitational force is: ) positive A) positive B) negative C) zero F N V T W Gravity is pushing against the direction of motion so it is negative. Lecture 15 Purdue University, Physics 149 8
Background image of page 8
ILQ 3 You are towing a car up a hill with constant velocity . The work done on the car by the tension force is: ) positive A) positive B) negative C) zero F N V T W The force of tension is in the same direction as the motion of the car, making the work positive. Lecture 15 Purdue University, Physics 149 9
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
ILQ 4 You are towing a car up a hill with constant velocity . The total work done on the car by all forces is: ) positive F N V A) positive B) negative C) zero T W The total work done is positive because the car is moving up the hill. (Not quite!) W=KE f -KE i =(0.5mv f 2 ) - (0.5mv i 2 ). Because the final and initial velocities are the same, there is no change in kinetic energy, and therefore no total work is done.
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/23/2011 for the course PHYS 149 taught by Professor Staff during the Spring '08 term at Purdue.

Page1 / 40

Lecture15 - PHYSICS 149: Lecture 15 Chapter 6: Conservation...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online