Units
Work & Power
Energy #1
Efficiency
Energy #2
100
What is the unit for distance or height?
M (Meters)
100
You push a piano with a force of 50 N and move it 2m. How much work have you actually done on the piano?
100 J
100
What is kinetic energy?
What is potential energy?
The energy from movement!
The energy when something is still, typically derived from the force of gravity.
100
You can increase a machine’s efficiency by decreasing the…
Friction!
100
The potential energy in a stretched spring is…
Mechanical Energy
200
What is the unit for mass?
G (Grams)
200
Crystal weighs 50 kg. She takes 4 seconds to carry a 10-kg suitcase up a flight of stairs 3 m high. What is her power?
441 W
200
When Ari draws back an arrow in a bow, it has a potential energy of 100 J. If the efficiency of the bow and arrow system is 75%, how much kinetic energy will the arrow have when it is launched?
75 J
200
A 60-W light bulb uses 60 J of electrical energy every second. However, only 6 J of electrical energy is converted each second!
What is the efficiency of this lightbulb? Give your answer as a percentage!
10%
200
Producers make Radiant Energy into...
Chemical Energy
300
What is the unit for velocity or speed?
M/s or meters per second
300
Sal has a weight of 500 N. How many joules of work has Sal done against gravity when he reaches 4 m high on a rock climbing wall?
19,600 J
300
A child on a sled is at rest at the top of a hill 10 m high. The child and sled combined have a mass of 20 kg. They sled down the hill and attain a speed of 12 m/s. How much energy was lost to friction when they slid down the hill and converted their potential energy to kinetic energy?
520 J
300
You build a machine which is 80% efficient. How many joules of work are put into the machine to produce 400 J of output work?
500 J
300
Name a natural system that can reach a steady state for energy flow!
The Hydrologic Cycle, Solar Energy, Food Chains, etc
400
What is the unit for acceleration?
M/s2 or meters per second squared
400
Alex weighs twice as much as Bob. Bob weighs twice as much as Carlos. They each climb a flight of stairs in the same amount of time. Who has more power?
You must explain WHY for full credit, otherwise you get half!
Alex, because the formula for power is work divided by time, and the formula for work is Force x Distance! Alex has done more work thanks to his weight.
400
Jack uses 30 Calories of energy to climb a hill. Their increase in potential energy is 9,800 J. What is their energy efficiency?
8%
400
An elevator carries a 50 kg person up 10 m. The elevator does 7000 kg of input work. What is the efficiency of the elevator?
70%
400
What does the second law of thermodynamics state?
When work is done by heat flowing, the output work must be less than the amount of heat flow.
500
What is the unit for Power?
What is the unit for Work?
(Bonus for 500 extra points, how many watts in a horsepower?)
W (Watts)
J (Joules)
746 Watts in a Horsepower500
Kyle’s system of pulleys is used to lift an elevator that weighs 3000 N. The pulley system uses three ropes to support the load. How far would 12,000 J of input work lift the elevator? Assume this system is frictionless!
4 meters!
500
At each level of the food pyramid (seen slightly below), about 90% of the usable energy is lost in the form of heat. Just like you all learned in Biology!
Which level requires the most overall input of energy to meet its energy needs?
Use the diagram and logic from energy levels to explain why a pound of steak costs more than a pound of corn!
Answers may vary!
500
A typical car is about 13% efficient at converting energy from gasoline to energy of motion. The average car today gets about 25 mi for each gallon of gas!
Name at least four energy transformations that occur in a car!
Name three things that contribute to lost energy, and prevent a car from ever being 100% efficient
Answers will vary!
500
Geo’s futuristic motorcycle has a mass of 2000 kg and a speed of 10 m/s. A force of 5000 N is applied!
What is their motorcycle’s kinetic energy?
What is the distance it takes to stop when they do the cool Akira bike slide?
100,000 J
20 m