Energy, Power, & Work

​Science Root of the Day:

DO NOW: Write what you think the example words mean in your lab manual.

Extra Credit: Find three additional words that use this root and write them and their definition in your lab manual (6 Points Max)

Work, Energy, & Power

Multiple Choice

In which part of the graph is the object slowing down?

• A

• B

• C

• D

Multiple Choice

The momentum of an object depends upon the object's ___________&_____________.  

• size and shape
• mass and speed
• mass and veloctiy
• mass and energy

Multiple Choice

Newton's third law states that any action will have a(n) _______ and ______ reaction

• Equal and similar

• Equal and opposite

• Equal and different

• Greater and opposite

Multiple Choice

The equation to calculate momentum is

• p=mv
• p=1/2mv²
• p=mgh
• p=mg

Multiple Choice

Which has more momentum: a car stopped at a red light or a bike moving at 15 mph?

• car
• bike
• they are equal
• cannot determine using the info provided

Multiple Choice

Collisions can be ____________or ___________.

• fast or slow
• far or near
• elastic or inelastic
• none of the above

Multiple Choice

A roller coaster's velocity at the top of a hill is 10m/s. 2 seconds later, it reaches the bottom of the hill with a velocity of 26 m/s. What was the acceleration of the coaster?

• 20 m/s

• 10 m/s2

• 8 $$\frac{m}{s^2}$$

• 16 m/s3

Multiple Choice

Which of the following has the greatest momentum?

• a scurrying cockroach

• a parked semi-truck

• more information is needed

Multiple Choice

An elephant and a feather fall through the air. The force of air resistance is greatest on the:

• elephant

• feather

• same

Lesson Objectives

• Describe how work done on an object relates to its change in energy

• Specify the relationship between work and power

• Describe the different types of energy

  • Specify the relationship between Potential energy and change in location

  • Relate Kinetic Energy to Velocity

Work​

• Work is the amount of effort it takes to make something move

  • Work = Force x Distance

    • The unit is the Newton-Meter, also known as the joule (J)

  • Work is done when a net force acts on an object and the object moves in the direction of the force

• We do work whenever we make something move

  • Moving a heavier mass requires​ more work because you need more force

Work​ Practice Problem 1

• How much Work is needed to lift an object that weighs 500 N to a height of 2 m?

  • Step 1: Identify your Variables

    • W= ?

    • F= 500 N

    • D= 2 meters

  • Step 2: Plug and Solve

    • W= 500 × 2

Work​ Practice Problem 2

• How much Work is needed to lift an object that weighs 500 N to a height of 4 m?

  • Step 1: Identify your Variables

    • W= ?

    • F= 500 N

    • D= 4 meters

  • Step 2: Plug and Solve

    • W= 500 × 4

Power

• Lifting a load quickly is more difficult than lifting the same one slowly

  • The force and distance don't change so why is this?

• Power is the rate at which energy changes from one form to another

  • Power = Work/time​=w/t

  • Unit is the watt (J/s)

• Think of an engine: A high-power engine can do work rapidly.

  • One with twice the power is not necessarily twice as fast

    • it can do twice as much work in the same amount of time OR it can do the same amount of work in half the time

Power Sample Problem 1

• How much power is expended when lifting a 1000 N load a distance of 4 m in 2 sec?

  • Step 1: Identify your Varaibles

    • W= F × d = 1000 × 4

    • t=2 sec

    • P=?

  • Step 2: Plug in and Solve

    • Power = 4000/2

Power Sample Problem 2

• A 20 N cart is pushed a distance of 3.5 meters and 140 Watts of power is expended. How long was the cart pushed for?

  • Step 1: Identify your variables

    • W= F × d

    • t=?

    • Power= 140 watts

Power Sample Problem 2

• A 20 N cart is pushed a distance of 3.5 meters and 140 Watts of power is expended. How long was the cart pushed for?

  • Step 1: Identify your variables

    • W= F × d= 20 × 3.5 = 70

    • t=?

    • Power= 140 watts

  • Step 2: Plug your Variables into your equation and solve

Mechanical Energy

• Energy: the ability to do work

  • Measured in joules

  • two types of energy

    • Potential energy

    • Kinetic energy​

Potential energy

• Potential energy is energy stored due to the position of the object

  • ​Example: think of a bow and arrow, as the archer pulls the bow back, the arrow is not yet moving but has the potential to do so once released

  • Example 2: Picture a car at the top of a hill just before it goes down.

Potential energy

• Gravitational Potential Energy: energy an object has due to being elevated

  • Is equal to the amount of work done against gravity

    • GPE= Force x height

    • GPE= mass x gravity x height​

  • Depends only on the distance to the ground, not necessarily the path to get there

Kinetic Energy

• Kinetic Energy: The energy of an object due to its motion

  • Can be transferred from one object to another

• Depends on the mass and speed of the object

  • Can only be a positive number

Kinetic Energy Sample Problem 1

• Calculate the Kinetic Energy of a 1-kg Parrot flying at 6 m/s.

  • Step 1: Identify your variables

    • m= 1 kg

    • v = 6 m/s

  • Step 2: Plug your variables into your equation and solve

Multiple Choice

A bicycle and a person with a total mass of 80 kg are traveling at a velocity of 7 m/s. What is their kinetic energy?

• 156,800 J

• 1,960 J

• 0.82 J

• 7,840 J

Conservation of Energy

• Energy is neither lost nor gained within a system

  • It changes from one form of energy to another

Open Ended

Can something have energy without having momentum? Can something have momentum without energy. Explain your answers