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Unit 3 Section 2 Energy and the Work-Energy Theorem. Unit 3 Work , Energy & Power. Serway Chapters 7 & 8 Glencoe Chapter 10 & 11. Unit 3 Section 2 Lesson 1 FEB 1 Kinetic Energy and the Work-Energy Theorem KE Objectives. Unit 3 Section 2 Lesson 1 Kinetic Energy Objectives :
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Unit 3 Section 2 Energy and the Work-Energy Theorem Unit 3 Work, Energy & Power Serway Chapters 7 & 8 Glencoe Chapter 10 & 11
Unit 3 Section 2 Lesson 1 FEB 1Kinetic Energy and the Work-Energy TheoremKE Objectives 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 • Do NOW: If you placed a 10.0 Kg object 1.5 m from the fulcrum of an ideal lever with an IMA of 4.0 what would the mass of the object needed to keep the lever balanced? • If you had to place a 3.0 kg mass to balance the lever what is the efficiency of the lever? • Unit 3 Section 2 Lesson 1 HOMEWORK: • Serway PAGE:209 : #’s 27, 30, 31, 33, 34, 37, 40, 41 • Glencoe Page 278 – 279: #’s 71, 72, 78 • Glencoe Page 283: #’s 1 – 7 all
Energy – Quick Re-cap • Energy is the capacity to do WORK • SI Unit: Joule (J) • Many forms • Common ones: • Kinetic • Potential • Electric • Chemical • Solar • Nuclear
Mass = m Velocity, V Kinetic Energy (KE) • 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
Examples of KE KE of van at 2m/s = ½ x 1000 x (2)2 = 2000 J = 2 kJ • 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 2000 x (2)2 = 4000 J = 4 kJ KE of van at 2m/s = ½ x 1000 x (4)2 = 8000 J = 8 kJ
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 Purple onto his truck using a 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
Unit 3 Section 2 Lesson 2Potential EnergyPE Objectives Unit 3 Section 2 Lesson 2 Potential Energy Objectives: • Show understanding of the Physics concept of Potential Energy • Correctly identify PotentialEnergy from given situations • Recall and show understanding of the formula to calculate PotentialEnergy • Show understanding of the relationship between PotentialandKineticEnergy • Do NOW: If you accelerate a 4.0 kg object from rest at 2.0 m/s2for 5.00 sec, what is the kinetic energy of the object? How much work was done on the object? • Unit 3 Section 2 Lesson 1 HOMEWORK: • Glencoe Page 307: #’s 58 – 72 ALL
Potential Energy • Potential energy is the energy possessed by an object as a result of its POSITION or CONDITION. • Gravitational PE {GPE} • In Physics, ground level is normally assumed to be at ZERO GPE. • Any object that is at ground level has ZERO GPE. • If object is lifted a certain height above ground, its GPE has increased. • Elastic PE (not in syllabus) • “Slinky” … when stretched or compressed • Spring … when stretched or compressed • Rubber band … when stretched • Balloon with air … when compressed
Object on top of building, of mass, m g earth Distance from ground, h Ground, 0 GPE Gravitational PE • Can be calculated with: GPE = mass gravitational height above acceleration ground level = mgh Units: [J] =[kg] * [m/s2] * [m] SI Units of GPE : Joule [J]
Example of GPE • You lifted your 5.0 Kg book bag to the top of your table. What can you say about the GPE of your bag? • Zero, increase, decrease • Lift the same bag on the Moon. What happens to GPE? • Zero, increase, decrease • Will the GPE be the same on Earth and Moon? • Same, less on Moon, more on Moon?
Examples of GPE • You lifted a set of books of mass 3.0 kg, for 2.0m. What is the GPE gained by the books? Take g=10m/s2. • Find the work done by you to lift the books. ΔUg = GPE = mgh = 3 10 2 = 60 J • Work done, W = F d (F = weight of books) • = (m g) d • = 3 x 10 x 2 • = 60 J (Note: same as GPE)
Unit 3 Section 2 Lesson 2 PE {ΔUg} In Class 290/1 • You Lift a 7.30 kg bowling ball from a storage rack and hold it up to your shoulder preparing to roll it down the lane for a STRIKE! The storage rack is 0.610 m above the floor and your shoulder is 1.12 m above the floor. • How much work did you do lifting the ball from the rack to your shoulder? • Nikita drops a 1.6 kg brick from the mansion roof 6.7 meters to the ground. • What was the change in potential energy? • A Warehouse worker picks up a 10.15 kg box from the floor and places it on a shipping table 1.15 meters above the ground. As he wraps the box for shipping, he slides it down the 3.5 m table to the end at a constant velocity in 21.0 seconds. He then lowers the box back to the floor . • Ignoring friction, what was the total energy change of the box? • Nikita drops a 1.6 kg brick from the mansion roof 6.7 meters to the ground. • If all the potential energy was converted into kinetic energy, what was the velocity of the brick (no friction) when it hit the ground?
Labs • Hooks LawAtwood’s MachineWork Energy and the Ramp
Hooks Law • Hooks Law PHET
