Unit 3 Work, Energy & Power Serway Chapters 7 & 8 Glencoe Chapter 10 & 11 1 Unit 3 Section 2 Energy and the Work-Energy Theorem

FEB 1 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: ▫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 2

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 3

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 (mv 2 )  [ J ] = [kg] [m/s] 2 Mass Doubles Kinetic Energy Doubles Velocity Doubles Kinetic Energy QUADRUPLES 4 Mass = m Velocity, V

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. 5 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

Work – Kinetic Energy Theorem Serway page 195 W = ∫ F dx  ∫ ma x dx Work = ΔKE = (½ mv 2 ) final – (½ mv 2 ) 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 6

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 ▫ 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 1 HOMEWORK: ▫ Glencoe Page 307: #’s 58 – 72 ALL 7

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 8

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] 9 Ground, 0 GPE Distance from ground, h Object on top of building, of mass, m g earth

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? 10

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. 11 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)

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 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 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? 12

Labs Hooks Law Atwood’s Machine Work Energy and the Ramp 13

Atwood’s Machine 14

Hooks Law Hooks Law PHET 15