WORK & ENERGY Work Work Energy Thm. Kinetic Energy Power Potential Energy Conservation of Energy

WORK & ENERGY Work Work Energy Thm. Kinetic Energy Power Potential Energy Conservation of Energy

WORK & ENERGY Work: Transfer of energy through motion Energy: Ability to cause Change Kinetic Energy: Energy Due to Motion For work to be done, a force must be exerted for a distance A component of force must be parallel to motion

WORK & ENERGY WORK: W = F d = Fdcosϴ (Scaler Dot Product) F*d = 1N *1m = 1 Joule

WORK & ENERGY (examples) An athlete pulls a 100kg sled a distance of 10m with a force of 320N at an angle of 15 o above the horizontal. How much work does he do? Some dude carries a 4 kg briefcase a distance of 4m at a constant speed. How much work does he do on the briefcase?

WORK & ENERGY (examples) A weight lifter raises a 100kg weight a distance of 2m at constant speed. How much work does he do? A weight lifter raises a 100 kg weight a distance of 2m at constant speed. How much work does gravity do? A weight lifter holds a 100 kg weight a distance of 2m above the ground. How much work is being done?

WORK & ENERGY THEOREM Sum of all work done on an object equals change in Kinetic Energy ΣW = KE v f2 = 2ad + vi 2 2ad = vf 2 vi 2 ad = v f 2 vi 2 2 m ad = ma d = Fd = (m) v f 2 vi 2 2 Fd = 1 2 mv f 2 1 2 mv i 2 KE = 1 2 mv2 Positive work done by person on shovel (Adds Energy to the system) Negative work done by friction on shovel (Removes Energy from the system)

WORK & ENERGY THEOREM EXAMPLES An athlete pulls a 100kg sled a distance of 10m with a force of 320N at an angle of 15 o above the horizontal. What is final velocity of the mass? W=3091J

WORK & ENERGY THEOREM EXAMPLES A Bow exerts a force of 200N on a 0.150kg arrow for a distance of 0.60m. What is the final velocity of the arrow?

WORK & ENERGY THEOREM EXAMPLES A weight lifter raises a 100 kg weight a distance of 2m at constant speed. How much work does he do? A weight lifter raises a 100 kg weight a distance of 2m at constant speed. How much work does gravity do? A weight lifter holds a 100 kg weight a distance of 2m above the ground. How much work is being done? A weight lifter holds a 100 kg weight a distance of 2m above the ground. What is the final velocity of the weights?

WORK & ENERGY THEOREM EXAMPLES A 1200 kg car moving at 15m/s skids to a stop in 20m. How much work required to stop the car? What is the coefficient of friction between the tires and the road?

POWER Power = Rate at which work is done Power = Work Time = W t = Fd t = Fv = Fvcosθ 1 J s = 1 watt = 1W 1Hp = 746 Watts

Power A weight lifter raises a 100 kg weight a distance of 2m at constant speed in 1.5 seconds. What is his power output? An athlete pulls a 100kg sled a distance of 10m in 5.5s with a force of 320N at an angle of 15 o above the horizontal. What is the power output?

Power Example: An Elevator can lift a maximum of 900kg at a rate of 1.5m/s. What is the power of the elevator

POWER Example: A 1500kg car can accelerate from 0-60mph in 3.8s. How much power does the car exert?

POWER How much weight can a 5 Hp motor lift 2m in 10 seconds? How many joules of energy does a 60 Watt light bulb use in one hour?

POTENTIAL ENERGY Potential Energy = Energy stored due to position (Stored Energy) Electric Potential Energy = energy due to position of electrons. Chemical Potential Energy = energy due to position of molecules. Nuclear Potential Energy = Energy stored due to position of Protons and Neutrons

Gravitational Potential Energy Energy due to position on a gravitational field Gravity can cause an object to fall Gravity has the ability to do work on an object The amount of work gravity can do is equal to the amount of potential energy W = Fd = mg h GPE = mgh=u g

Elastic Potential Energy Energy stored in the shape of an object As the shape of an object changes, it has the ability to do work in order to return to its original position Stretching a rubber band Compressing a Spring Bending a Ruler Pole Vaulting

Elastic Potential Energy Hooke s Law: Force required to stretch Ideal spring k= spring constant, x = displacement from rest position. Work done on spring = w = 1 2 kx2 Elastic Potential Energy = Work done on Spring EPE = 1 2 kx2

Conservation of Energy Total energy of a closed system remains constant. Energy cannot be created or destroyed, it only changes forms KE 1 + U 1 = KE 2 + U 2

Conservation of Energy A 150 kg rollercoaster car initially at rest rolls down a 50m hill. a) How much work was done to get the car to the top of the hill? b) How fast will it be moving at bottom of the hill? c) How fast will the car be moving at the top of the second hill 25m high?

Conservation of Energy A sling shot is stretched a distance of 2.5m with a force of 300N. What is the spring constant of the sling shot? How much work was done on the sling shot? How fast will a 2.0kg water balloon be moving after it is fired horizontally from the slingshot? If it is shot in the vertical direction, How high will it go?

Conservation of Energy A high jumper run at a speed of 8 m/s, and jumps to height of 2.5m. What is his velocity at maximum height? What could be his maximum height?

Conservation of Energy Mass of bear = 50kg Height Bear falls Spring displacement = 0.75m Spring constant k of trampoline?