Work, Power and Energy

WORK Is the

production of force and distance

Work is done when a force acts on an object in the direction the object moves.

No movement, no work is done

Work Formula

Work = Force x distance

W= F x d Unit for Work= joule (J)

Work Practice1. A man weighing 750 N climbs a flight of stairs 5

m high. How much work has he done?

2. A 10 N book is raised 500 meters from the floor. How much work is done?

3. Kayla does 40 J of work while pushing a shopping cart 30 meters. What is the force applied?

4. David pulls a 450 N sofa up the stairs producing 25 J of work. How far did he pull the sofa?

5. A 100 kg object is pulled vertically upward 5.0 m by a rope with an acceleration of 1.0 m/s2. Find the work done by the tension force in the rope.

Power Rate of doing

work Doing work at a

faster rate requires more work.

To increase power, you can increase the amount of work done in a given time.

Power Formula:

Power= Work/time (s)P = W/t

Unit: J/s or Watt

Power Practice1. A motorcycle does 2000 J of work in 25

seconds. How much power is produced?

2. Sean does 125 J of work in 50 seconds. How much power is produced?

3. Kayla produced 20 W of power in 0.5 seconds. How much work was done?

4. Jacob does 400 J of work to produce 15 W of power. How long did he work?

5. Beth moves a 15 N book 20 meters in 10 seconds. How much power was produced?

Energy

The ability to do work.

Measured in Joules (J)

Two typesKineticPotential

Kinetic Energy

The energy of motion The kinetic energy of any moving

object depends upon its mass and speed

Measured in Joules (J)Formula: KE = ½ m v2

Kinetic Energy Practice

1. A 3 kg ball is rolling 2 m/s. How much kinetic energy does it have?

2. Determine the kinetic energy of a 625-kg roller coaster car that is moving with a speed of 18 m/s.

3. A 30-kg car is going down a hill with a speed of 5 m/s. What is the cars kinetic energy?

Potential Energy Is the energy that is stored as a result of

position or shape Gravitational Potential Energy—

potential energy based on heightAn object’s gravitational potential energy

depends on its mass, its height, and the acceleration due to gravity

Formula: GPE = m x g x hm=massg= acceleration due to gravity (9.8 m/s/s)h=heightUnit: Joule

Potential Energy Practice1. A 4 kg rock is sitting on a 3 m

ledge. How much potential energy does it have?

2. A 625-kg roller coaster is sitting at the top of the hill 90 meters from the ground. What is the coaster’s potential energy?

3. A book has 40 J of potential energy when it is 5 meters from the ground. What is the book’s mass?

Types of Energy Transfer

Mechanical: energy in motion

ex: water falls, car Thermal: internal motion of

particles ex: fire Chemical: chemical

changes and bonds ex: lighting a match,

chemical reactions Nuclear: splitting of atoms ex: sun Electromagnetic: electrical

charges ex: spectrum, light

waves, electromagnets

Energy Conservation

Energy cannot be created or destroyed

Energy Conversions The gravitational potential energy of an object

is converted to the kinetic energy of motion as the object falls

P.E. greatest

K.E. greatest

P.E. greatest

conversion

Pendulums and energy

1. P.E. greatest

2. P.E. decreases and K.E. increases

3. K.E. greatest

4. K.E. decreases and P.E. increases

5. P.E. greatest

Projectile Motion Projectile Motion site When an object has a forward force and

gravity affecting its path. How many forces are acting on it?

TWO (Forward and gravity) Ex: baseball, bullet from a gun