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/s2) Displacement – Meter Work – Joule (kg*m2/s2) – (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 X+ Fx

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” What is W? m = 2800kg F = 29N d = 500m What is W? Y+ d X+

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

Work and Energy Work Problem “Building Moving” m = 6600kg d = 2.5m What is the Amount of Work?

Work and Energy Work Solution “Building Moving” m = 6600kg d = 2.5m

Work and Energy Work Solution “Building Moving” m = 6600kg d = 2.5m F = 6.5x104N

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

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

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 20N for 5m, then 35N for 12m, then 10N for 8m. What is the work that John has done pushing the box?

Work and Energy Work Solution d1 = 5m F1 = 20N d2 = 12m F2 = 35N

Work and Energy Work Solution

Work and Energy Work Problem A pump delivers 0.55m3 of oil into barrels on a platform 25.0m above the pump intake pipe. The density of the oil is 0.82g/cm3. What is the work done by the pump?

Work and Energy Work Solution d = 25.0m volume = 0.55m3 density = 0.82g/cm3 mass = ?

Work and Energy Work Solution d = 25.0m volume = 0.55m3 density = 0.82g/cm3 mass = ?

Work and Energy Work Solution d = 25.0m volume = 0.55m3 density = 0.82g/cm3 mass = 4.5x102kg F = ?

Work and Energy Work Solution d = 25.0m volume = 0.55m3 density = 0.82g/cm3 mass = 4.5x102kg F = 4.4x103N

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

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

Work and Energy Solution vo = 0m/s vf = 6.9m/s d = 300m q = 150 m = 682kg Fx = ? F = ?

Work and Energy Solution vi = 0m/s vf = 6.9m/s d = 300m q = 150 m = 682kg Fx = ? F = ?

Work and Energy Solution vi = 0m/s vf = 6.9m/s d = 300m q = 150 m = 682kg Fx = 54N 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 25km/hr in 300m. The angle of the rope is 150. The race car’s mass is 682kg. What is the work done? Y+ Fy F q X+ Fx

Work and Energy Solution vi = 0m/s vf = 6.9m/s d = 300m q = 150 m = 682kg Fx = 54N F = 55.9N

Work and Energy Solution vi = 0m/s vf = 6.9m/s d = 300m q = 150 m = 682kg F = 54N

Work and Energy Solution vi = 0m/s vf = 6.9m/s d = 300m q = 150 m = 682kg F = 54.6N

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) 1J=1kg*m2/s2

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

Work and Energy Work Solution m = 2800kg F = 29N d = 500m 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 (53J, ?) 9 (47.5J) 11 (?, ?, ?) 23 (a, 5400J, 0J, 5400J b, 0J, -5400J, 5400J c, 2700J, -2700J, 5400J) 25 (a, 0.4J b, 0.225J, c, 0J)

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) Units are Watts 1 watt = 1 J/s

Work and Energy Power (P) Problem: “Lift that Barge” Ryan 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) Solution: “Lift that Barge” d = 22m m = 90.7kg t = 3x102s

Work and Energy Power (P) Solution: “Lift that Barge” d = 22m m = 90.7kg t = 3x102s

Work and Energy Power (P) Solution: “Lift that Barge” d = 22m m = 90.7kg t = 3x102s F = 8.9x102N

Work and Energy Power (P) Solution: “Lift that Barge” d = 22m m = 90.7kg t = 3x102s F = 8.9x102N

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

Work and Energy Power (P) Solution: “Lift that Barge” d = 22m m = 90.7kg t = 20s F = 8.9x102m

Work and Energy Power (P) Solution: “Lift that Barge” d = 22m m = 90.7kg t = 20s F = 8.9x102m

Work and Energy Power (P) WOW! To Move the Piano in 5 Minutes – 65w To Do the Same Work in 20 seconds – 979w Yes, 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 = 300N d = 30.0m m = 145kg t = 3.0s

Work and Energy Problem April pushes a wheelbarrow by exerting a 145N force horizontally. April moves it 60.0m at a constant speed for 25.0s. What power does April develop?

Work and Energy Solution F = 145N d = 60.0m t = 25.0s

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

Work and Energy Solution F = 145N d = 60.0m t = 12.5s

Work and Energy Problem Jon pulls a 305N sled along a snowy path using a rope that makes a 45.0° angle with the ground. Jon pulls with a force of 42.3N. The sled moves 16m in 3.0s. What power does Jon produce?

Work and Energy Solution Fg = 305N F = 42.3N d = 16.0m t = 3.0s q = 450

Work and Energy Problem A lawn roller is pushed across a lawn by a force of 115N along the direction of the handle, which is 22.5° above the horizontal. If you use 64.6w of power for 90.0s, what distance is the roller pushed?

Work and Energy Solution F = 115N P = 64.6w t = 90.0s q = 22.50

Work and Energy Problem You slide a crate up a ramp at an angle of 30.0° by exerting a 225N 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 1.15m?

Work and Energy Solution F = 225N mk = 0.28 h = 1.15m 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 6.0x103N to balance the force that water exerts against the hull. What power does the engine develop?

Work and Energy Solution F = 6.0x103N v = 15m/s

Work and Energy Problem A 188W motor will lift a load at the rate (speed) of 6.50cm/s. How great a load can the motor lift at this rate?

Work and Energy Solution P = 188W v = 6.5cm/s = 0.065m/s

Work and Energy Homework: Pages 195 – 197 Problems 33 (12.0m/s) 49 (a, 2.25x104N b, 1.33x10-4s) 57 (a, 4.4m/s b, 1.5x105N)