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Unit 3 Section 2 Lesson 2 Potential Energy PE Objectives Unit 3 Section 2 Lesson 2 Potential Energy Objectives: ▫ Show understanding of the Physics concept of Potential Energy ▫ Correctly identify Potential Energy from given situations ▫ Recall and show understanding of the formula to calculate Potential Energy ▫ Show understanding of the relationship between Potential and Kinetic Energy ▫ PE = mgh ▫ Do NOW: If you accelerate a 4.0 kg object from rest at 2.0 m/s 2 for 5.00 sec, what is the kinetic energy of the object? How much work was done on the object? ▫ Unit 3 Section 2 Lesson 2 HOMEWORK: ▫ Serway Pages 240 – 241 #’s 3, 5, 7, 13, 15, 21-22 ▫Unit 3 Section 2 Lesson 1 HOMEWORK: DUE MON Jan 14 ▫Serway PAGE:209 : #’s 27, 30, 31, 33, 34, 37, 40, 41 1

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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 2

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In Class Gravitational PE Can be calculated with: GPE = mass gravitational height above acceleration ground level = mgh Units: [J] =[kg] * [m/s 2 ] * [m] SI Units of GPE : Joule [J] 3 Ground, 0 GPE Distance from ground, h Object on top of building, of mass, m g earth

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In Class 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? 4

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In Class 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/s 2. Find the work done by you to lift the books. 5 ΔU g = 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)

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Unit 3 Section 2 Lesson 2 PE {ΔU g } 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? Elliot 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? Elliot 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? 6

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