Work Transfers Energy
(Part 1)
Work Transfers Energy
(Part 2)
Conservation of Energy
Power from Work
Power from Energy
100
What do we call energy of motion?
kinetic energy
100
What do we call stored energy?
potential energy
100
What states the following: "no matter how energy is transferred or transformed, all of the energy is still present in one form or another"?
the law of conservation of energy
100
What is power?
Power is the rate at which work is done
100
What unit do we use to measure power?
watt
200
What do we call an objects total kinetic and potential energy combined?
mechanical energy
200
What unit do we use to measure energy?
Joules
200
Why doesn't a pendulum continue to swing back and forth forever?
There is friction (air resistance)
200
How many watts is equal to one horsepower?
745 watts
200
When would it be useful to think of power as the transfer of energy in a certain amount of time?
when you cannot measure the work used to transfer the energy, such as with a television set
300
For what two reasons would an object have potential energy? (due to its _____ and _______)
shape and position
300
How are work and energy related?
When work is done, energy is transferred
300
Give one example of mechanical energy being conserved (you can ignore friction).
Examples will vary - a skater on a ramp
300
What is horsepower? When would we use horsepower?
It is the amount of work a horse can do in a minute. It is used to describe the amount of power engines have (i.e. car, airplane, etc.)
300
Which lightbulb needs a higher transfer of energy per second - a 60 W bulb or 100 W bulb? Explain.
The 100 W bulb because 100 W means the bulb needs 100 J of energy transferred per second for it to work.
400
What is the formula for finding gravitational potential energy? Make sure to explain each part of the equation.
GPE = mgh (m = mass, g = acceleration due to gravity, and h = height).
400
What is the kinetic energy of a boy who has a mass of 20kg and a velocity of 2 m/s?
KE = 1/2 mv^2 = 1/2(20kg)(2m/s)^2 = 40 J
400
Explain in detail how kinetic energy and potential energy change relative to each other as a skater rides on a ramp.
At the top of the ramp, the skater has no kinetic energy and 100% potential energy. Halfway down the ramp 50% of energy is potential and 50% is kinetic. At the bottom 100% of energy is kinetic and 0% is potential.
400
If a conveyor belt uses 10 J to move a piece of candy a distance of 3 m in 20 s, what is the conveyor belt's power?
P = W/t = 10J/20s = 0.5 W
400
A laptop computer uses 100 J every 2 seconds. How much power is needed to run the computer?
P = E/t = 100J/2s = 50 W
500
A truck with a mass of 6000 kg is traveling north on a highway at a speed of 17 m/s. A car with a mass of 2000 kg is traveling south on the same highway at a speed of 30 m/s. Which vehicle has more kinetic energy?
KE of truck = 1,734,000 J KE of car = 1,800,000 J KE of car is higher
500
If you lift a 2 kg box of toys to the top shelf of a closet, which is 3 m high, how much gravitationa potential energy will the box of toys have?
GPE = mgh = (2kg)(9.8m/s^2)(3m) = 58.8 J
500
List the five types of energy and briefly explain each one
1) Mechnical - energy due to an object's motion and position 2) Thermal - energy an object has because of the motion of its molecules 3) Chemical - energy stored in chemical bonds 4) Nuclear - potential energy stored in the nucleus of an atom 5) Electromagnetic - electrical and magnetic interactions (electricity).
500
An elevator uses a force of 1710 N to life 3 people up 1 floor. Each floor is 4 m high. The elevator takes 8 s to life the 3 people up 2 floors. What is the elevator's power?
P = W/t = (F)(d)/t = (1710 N)(8m)/8s = 1710 W
500
The power needed to pump blood through your body is about 1.1 W. How much energy does your body use when pumping blood for 10 seconds?
P = E/t E = (P)(t) = (1.1W)(10s) = 11 J
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