work, power and energy. work is the production of force and distance work is done when a force...
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Work, Power and Energy
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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
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Work Formula
Work = Force x distance
W= F x d Unit for Work= joule (J)
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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.
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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.
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Power Formula:
Power= Work/time (s)P = W/t
Unit: J/s or Watt
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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?
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Energy
The ability to do work.
Measured in Joules (J)
Two typesKineticPotential
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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
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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?
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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
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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?
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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
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Energy Conservation
Energy cannot be created or destroyed
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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
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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
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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