Physics Chapter 5 Work Energy Work

Physics Chapter 5: Work & Energy

Work and Energy • Work – A Force that Causes the Displacement of an Object Does Work on the Object

Work and Energy • Work – Has Direction (+ or -) • May Increase Energy of the System (+) • May Decrease Energy of the System (-)

Work and Energy • Work – Units • Force – Newton (kg*m/s 2) • Displacement – Meter • Work – Joule (kg*m 2/s 2) – (Nm)

Work and Energy • Work – A Horizontal Component of the Force (Relative to Motion) Must Do the Work

Work and Energy • Work – Work Done at an Angle • Forces Only Move in One Direction, but Involve 2 Axis • These Axis Vectors Can Be Separated and Calculated Individually Y+ F X+

Work and Energy • Work – Work Done at an Angle Y+ F Fy q Fx X+

Work and Energy • Work – Work Done at an Angle Y+ F q X+ Fx

Work and Energy • Work – Work Done at an Angle Y+ q F Fy q X+

Work and Energy • Work – Work Done at an Angle • May be Negative Y+ Fx X+ q Fy F

Work and Energy • Work – Work Done at an Angle • To Calculate Work Y+ Fx X+ q Fy F

Work and Energy • Work • Problem “Work Truck” – m = 2800 kg – F = 29 N – d = 500 m • What is W? Y+ d X+

Work and Energy • Work • Solution – m = 2800 kg – F = 29 N – d = 500 m Y+ d X+

Work and Energy • Work • Problem “Building Moving” – m = 6600 kg – d = 2. 5 m • What is the Amount of Work?

Work and Energy • Work • Solution “Building Moving” – m = 6600 kg – d = 2. 5 m

Work and Energy • Work • Solution “Building Moving” – m = 6600 kg – d = 2. 5 m – F = 6. 5 x 104 N

Work and Energy • Work • Problem – The third floor of a house is 8 m above street level. How much work is needed to move a 150 kg refrigerator to the third floor?

Work and Energy • Work • Solution – d = 8 m – m = 150 kg

Work and Energy • Work • Problem – John pushes a box across the floor of a stage with a horizontal force. The roughness of the floor changes, and John must exert a force of 20 N for 5 m, then 35 N for 12 m, then 10 N for 8 m. What is the work that John has done pushing the box?

Work and Energy • Work • Solution – d 1 = 5 m – F 1 = 20 N – d 2 = 12 m – F 2 = 35 N – d 3 = 8 m – F 3 = 10 N

Work and Energy • Work • Solution

Work and Energy • Work • Problem – A pump delivers 0. 55 m 3 of oil into barrels on a platform 25. 0 m above the pump intake pipe. The density of the oil is 0. 82 g/cm 3. What is the work done by the pump?

Work and Energy • Work • Solution – d = 25. 0 m – volume = 0. 55 m 3 – density = 0. 82 g/cm 3 – mass = ?

Work and Energy • Work • Solution – d = 25. 0 m – volume = 0. 55 m 3 – density = 0. 82 g/cm 3 – mass = ?

Work and Energy • Work • Solution – d = 25. 0 m – volume = 0. 55 m 3 – density = 0. 82 g/cm 3 – mass = 4. 5 x 102 kg –F=?

Work and Energy • Work • Solution – d = 25. 0 m – volume = 0. 55 m 3 – density = 0. 82 g/cm 3 – mass = 4. 5 x 102 kg – F = 4. 4 x 103 N

Work and Energy • Problem – Ryan pulls his race car with a rope from his personal car. He accelerates from rest to a speed of 25 km/hr in 300 m. The angle of the rope is 15 o. The race car’s mass is 682 kg. What is the force on the rope? Y+ Fy F q X+ Fx

Work and Energy • Solution – – – 25 km/hr d = 300 m q = 150 m = 682 kg Fx = ? F=?

Work and Energy • Solution – – – – vo = 0 m/s vf = 6. 9 m/s d = 300 m q = 150 m = 682 kg Fx = ? F=?

Work and Energy • Solution – – – – vi = 0 m/s vf = 6. 9 m/s d = 300 m q = 150 m = 682 kg Fx = ? F=?

Work and Energy • Solution – – – – vi = 0 m/s vf = 6. 9 m/s d = 300 m q = 150 m = 682 kg Fx = 54 N F=?

Work and Energy • Problem – Ryan pulls his race car with a rope from his personal car. He accelerates from rest to a speed of 25 km/hr in 300 m. The angle of the rope is 150. The race car’s mass is 682 kg. What is the work done? Y+ Fy F q X+ Fx

Work and Energy • Solution – – – – vi = 0 m/s vf = 6. 9 m/s d = 300 m q = 150 m = 682 kg Fx = 54 N F = 55. 9 N

Work and Energy • Solution – – – vi = 0 m/s vf = 6. 9 m/s d = 300 m q = 150 m = 682 kg F = 54 N

Work and Energy • Solution – – – vi = 0 m/s vf = 6. 9 m/s d = 300 m q = 150 m = 682 kg F = 54. 6 N

Work and Energy • Energy – The Ability to Produce Change Within a System • Thermal Energy • Chemical Energy • Energy of Motion

Work and Energy • Energy – Energy of Motion • The Energy of an Object Resulting from Motion • Kinetic Energy

Work and Energy • Energy – Kinetic Energy • Kinetics • Newton’s Second Law of Motion

Work and Energy • Energy – Kinetic Energy • Kinetics • Motion Equation – – Vi is initial velocity Vf is the final velocity a is the instantaneous acceleration d is the displacement

Work and Energy • Energy – Kinetic Energy • Kinetics

Work and Energy • Energy – Kinetic Energy (K) • Kinetics

Work and Energy • Energy – Kinetic Energy (K) • Kinetics Energy of the System = Environment

Work and Energy • Energy – Kinetic Energy (K) • Kinetics System (Change in Energy) = Environment (Object) A Change in the Environment Due to Energy = Work

Work and Energy • Energy – Kinetic Energy (K) • Kinetics A Change in the Environment Due to Energy = Work

Work and Energy • Energy – Kinetic Energy (K) • Kinetics – Work-Energy Theorem

Work and Energy • Energy – Kinetic Energy • Units – Joule (J) – 1 J=1 kg*m 2/s 2

Work and Energy • Work • Problem “Work Truck” – m = 2800 kg – F = 29 N – d = 500 m • What is DKE? Y+ d X+

Work and Energy • Work • Solution – m = 2800 kg – F = 29 N – d = 500 m Y+ d X+

Work and Energy • Energy – Potential Energy (Gravitational) • Any Object Held by a Normal Force Against the Force of Gravity Contains Potential Energy

Work and Energy • Energy – Potential Energy (Gravitational) • The product of… – the Mass of the Object – the Acceleration of Gravity – the Height of the Object

Work and Energy • Energy – Potential Energy (Elastic)

Work and Energy • Homework – Page 193 - 194 • Problems – 7 (53 J, ? ) – 9 (47. 5 J) – 11 (? , ? ) – 23 (a, 5400 J, 5400 J b, 0 J, -5400 J, 5400 J c, 2700 J, -2700 J, 5400 J) – 25 (a, 0. 4 J b, 0. 225 J, c, 0 J)

Work and Energy • Energy – Conservation of Energy • An Object’s Potential Energy is Equal to its Kinetic Energy When the Normal Force is Released

Work and Energy • Energy – Conservation of Energy

Work and Energy • Energy – Conservation of Energy

Work and Energy • Energy – Conservation of Energy

Work and Energy • Power – Work Can be Done Quickly, or… – The Same Work Can be Done Over a Long Period of Time – Power is the Rate of Doing Work (the rate of energy transferred)

Work and Energy • Power (P) W = Work (Joules) t =Time (sec) “The Less Time, the Greater the Power”

Work and Energy • Power (P) ØUnits are Watts Ø 1 watt = 1 J/s

Work and Energy • Power (P) ØProblem: “Lift that Barge” ØRyan Hauls His Piano Up Two Flights of Stairs (22 m) in 5 minutes. The Piano’s mass is 90. 7 kg. What Power is Used?

Work and Energy • Power (P) ØSolution: “Lift that Barge” Ød = 22 m Øm = 90. 7 kg Øt = 3 x 102 s

Work and Energy • Power (P) ØSolution: “Lift that Barge” Ød = 22 m Øm = 90. 7 kg Øt = 3 x 102 s

Work and Energy • Power (P) ØSolution: “Lift that Barge” Ød = 22 m Øm = 90. 7 kg Øt = 3 x 102 s ØF = 8. 9 x 102 N

Work and Energy • Power (P) ØSolution: “Lift that Barge” Ød = 22 m Øm = 90. 7 kg Øt = 3 x 102 s ØF = 8. 9 x 102 N

Work and Energy • Power (P) ØProblem: “Lift that Barge II” ØWhat If Ryan Hustled the Piano Up the Stairs in 20 seconds?

Work and Energy • Power (P) ØSolution: “Lift that Barge” Ød = 22 m Øm = 90. 7 kg Øt = 20 s ØF = 8. 9 x 102 m

Work and Energy • Power (P) ØSolution: “Lift that Barge” Ød = 22 m Øm = 90. 7 kg Øt = 20 s ØF = 8. 9 x 102 m

Work and Energy • Power (P) ØWOW! ØTo Move the Piano in 5 Minutes – 65 w ØTo Do the Same Work in 20 seconds – 979 w ØYes, 20 seconds is 1/15 of the original 5 minute time and 65. 3 x 15 = 979. Hey! A Direct (linear) Relationship!

Work and Energy • Problem – A force of 300. 0 N is used to push a 145 -kg mass 30. 0 m horizontally in 3. 00 s. What is the power developed?

Work and Energy • Solution – F = 300 N – d = 30. 0 m – m = 145 kg – t = 3. 0 s

Work and Energy • Problem – April pushes a wheelbarrow by exerting a 145 N force horizontally. April moves it 60. 0 m at a constant speed for 25. 0 s. What power does April develop?

Work and Energy • Solution – F = 145 N – d = 60. 0 m – t = 25. 0 s

Work and Energy • Problem – If April moves the wheelbarrow twice as fast, how much power is developed?

Work and Energy • Solution – F = 145 N – d = 60. 0 m – t = 12. 5 s

Work and Energy • Problem – Jon pulls a 305 N sled along a snowy path using a rope that makes a 45. 0° angle with the ground. Jon pulls with a force of 42. 3 N. The sled moves 16 m in 3. 0 s. What power does Jon produce?

Work and Energy • Solution – Fg = 305 N – F = 42. 3 N – d = 16. 0 m – t = 3. 0 s – q = 450

Work and Energy • Problem – A lawn roller is pushed across a lawn by a force of 115 N along the direction of the handle, which is 22. 5° above the horizontal. If you use 64. 6 w of power for 90. 0 s, what distance is the roller pushed?

Work and Energy • Solution – F = 115 N – P = 64. 6 w – t = 90. 0 s – q = 22. 50

Work and Energy • Problem – You slide a crate up a ramp at an angle of 30. 0° by exerting a 225 N force parallel to the ramp. The crate moves at constant speed. The coefficient of friction is 0. 28. How much work have you done on the crate when it is raised a vertical distance of 1. 15 m?

Work and Energy • Solution – F = 225 N – mk = 0. 28 – h = 1. 15 m – q = 30. 00

Work and Energy • Problem – An engine moves a boat through the water at a constant speed of 15 m/s. The engine must exert a force of 6. 0 x 103 N to balance the force that water exerts against the hull. What power does the engine develop?

Work and Energy • Solution – F = 6. 0 x 103 N – v = 15 m/s

Work and Energy • Problem – A 188 W motor will lift a load at the rate (speed) of 6. 50 cm/s. How great a load can the motor lift at this rate?

Work and Energy • Solution – P = 188 W – v = 6. 5 cm/s = 0. 065 m/s

Work and Energy • Homework: – Pages 195 – 197 • Problems – 33 (12. 0 m/s) – 35 (17. 2 s) – 49 (a, 2. 25 x 104 N b, 1. 33 x 10 -4 s) – 57 (a, 4. 4 m/s b, 1. 5 x 105 N)