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Unit 3 Work, Energy & Power

Serway Chapters 7 & 8

Unit 3 Section 2 Energy and the Work-Energy Theorem

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Unit 3 Section 2 Lesson 1 Kinetic Energy and the Work-Energy Theorem

Unit 3 Section 2 Lesson 1 Kinetic Energy Objectives:▫ Show understanding of the Physics concept of Kinetic Energy▫ Correctly identify Kinetic Energy from given situations▫ Recall and show understanding of the formula to calculate Kinetic Energy▫ Solve related problems involving Change in Kinetic Energy

▫ KE = ½ mv2 ▫ Work = ΔKE = (½ mv2)final – (½ mv2)initial

▫ Do NOW: Charles is vacuuming room 3. He pushes the vacuum with a 5.00 N force at an angle of 30.0 degrees to the horizontal. If he pushes the vacuum 3.00 meters across the carpet, what is the work he did?

▫ Unit 3 Section 2 Lesson 1 HOMEWORK: DUE MON Jan 14▫ Serway PAGE:209 : #’s 27, 30, 31, 33, 34, 37, 40, 41

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Energy – •Energy is the capacity to do WORK•SI Unit: Joule (J)•Many forms•Common ones:

▫Kinetic▫Potential▫ Electric▫ Chemical▫ Solar▫ Nuclear

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Kinetic Energy KE = ½ (mv2)• A form of energy that a body in motion possess.• Examples:

▫ Bullet shot out from pistol▫ Helicopter flying at 120km/h

• A body a rest, will NOT possess any KE!• The amount of KE of a moving body depends on:

▫ Mass of body (kg)▫ Velocity (m/s)

• When either mass or velocity of moving body is increased, KE will also increase.• Kinetic Energy = ½ (Mass)(Velocity)2 = ½ (mv2) [ J ] = [kg] [m/s]2

• Mass Doubles Kinetic Energy Doubles• Velocity Doubles Kinetic Energy QUADRUPLES

Mass = m

Velocity, V

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DO NOW: Examples of KE• Find the KE of an empty van of mass 1000kg moving at

2m/s.

• Find the KE of van when it is loaded with goods to give a total mass of 2000kg, and moving at 2m/s.

• Find KE of unloaded van when it speeds up to 4m/s.

KE of van at 2m/s = ½ x 1000 x (2)2

= 2000 J = 2 kJ

KE of van at 2m/s = ½ x 2000 x (2)2

= 4000 J = 4 kJ

KE of van at 2m/s = ½ x 1000 x (4)2

= 8000 J = 8 kJ

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Work – Kinetic Energy Theorem• Serway page 195 • W = ∫ F dx ∫ max dx

•Work = ΔKE = (½ mv2)final – (½ mv2)initial

• If you push a 6.0 Kg object from rest along a frictionless surface with a force of 12.0 N what will the velocity be after 3 meters?

• Romac loads a refrigerator for Claire onto his truck using a frictionless ramp. He claims that less work is required to load the truck if the ramp is lengthened. Is he correct?

• Serway page 196 Exp 7.7 – 7.8

CY:3.5 AL: 3.6 CC: 3.4 EW: 2.8 PP:0.0 DH: 3.1