Energy
___________ is the energy of an object in motion
Kinetic energy
When a ball is thrown directly upward, which of the following is true?
Its kinetic energy is mostly converted to potential energy.
Its potential energy is mostly converted to kinetic energy.
Its kinetic energy is mostly converted to heat.
1. Its kinetic energy is mostly converted to potential energy.
Work is a measure of _____________
How much energy is transferred to an object in causing it to move.
Daily Double!
Place your wager!
Which of the following is not a definition of power?
The rate of energy transfer
How many Joules are converted to other forms of energy
The rate at which work is done
How quickly energy is converted
2. How many Joules are converted to other forms of energy (this is a definition of work)
If the amount of force in each is applied, which letter does the most work? (Square with fingers)
Draw on Board, C
Pulling back a rubber band is a form of storing __________ energy
Potential
If energy can be neither created nor destroyed, what do we mean when we say “Don’t waste energy!” What is the name of the “Wasted” energy?
Dissipated Energy
One unit for work is a Joule. A Joule is equivalent to a _______________
Write on board
Which is more powerful, a student that runs up the stairs or a student that walks? Assume they have equal mass.
A student that runs. Same work, less time.
Work has the same units as what other quantity?
Energy
Energy is a measure of an object’s _________________
Ability to cause change
When a car rolls down a hill, most of its potential energy converts to kinetic energy. Where does most of the rest of it go?
Heat (from friction)
How much work is done if a 20 N force is used to slide a box 4 meters?
80 J
Calculate the power of a machine that can do 2400 J of work in 8 seconds.
300 W
Complete the sentence:
Energy can never be created or destroyed, just __________
Energy can never be created or destroyed, just converted from one form to another.
What is the kinetic energy of a 15 kg boulder resting at the top of a 12 m cliff?
0 J (Not moving = no kinetic energy)
A 2 kg object sits at the top of a 10 m hill. How fast will it be rolling at the bottom of the hill?
14 m/s
How much work is done if Mr. Wondersr pushes against a boulder with 200 N of force for 5 seconds but the boulder doesn’t move?
0 J
How much energy does a 1500 W microwave use if it is on for 40 seconds?
60,000 J
A 1000 kg car and an 1200 kg car roll down a hill. Assuming energy is conserved, which car, if either, will be rolling faster at the bottom of the hill?
Neither. Gravity accelerates all objects the same regardless of mass.
What is the potential energy of a 15 kg boulder resting at the top of a 12 m cliff?
1764 J
An object starting with 20 J of potential energy rolls down a hill. At the bottom, 7/8 of the potential energy has been converted to kinetic energy. How much energy (in Joules) was “lost” due to friction?
2.5 J
How much work is done to lift a 40 kg barbell to a height of 2 m?
784 J
How powerful is a weight lifter who lifts a 400N weight 2 m in 1.6 seconds?
500 W
An ice skater is gliding across the ice at a constant speed. Is she doing work?
No. No acceleration means no force. No force means no work.