Introduction to Energy
What is the difference between kinetic energy and potential energy?
Kinetic energy is the energy of motion
Potential energy is a type of energy that is stored in an object due to its position relative to other objects
What is the formula for kinetic energy and what do the variables stand for?
KE= 1/2 mv^2
m=mass
v=velocity
What is the formula for potential energy and what do the variables stand for?
PE=mgh
m=mass
g=gravity (9.8 m/s^2)
h=height
any region in which a non-contact force has an effect
A person moves a ball up a ramp. Which statement describes this process?
A. There is no transfer of energy or work done.
B. There is a transfer of energy, and work is done.
C. There is no transfer of energy, but work is done.
D. There is a transfer of energy, but no work is done.
B. This is correct because energy is transferred from the person’s hand to the ball as it moves up the ramp, and work is done because the ball has moved.
What is work?
Work is defined as the transfer of energy to an object by a force that causes the object to move in the direction of that force
What two factors affect kinetic energy and which variable has a stronger affect?
The kinetic energy of an object depends on both the mass and speed of an object
KE of an object is directly proportional to the square of the speed of the object. If the speed of an object doubles, its KE quadruples.
Which diagram models the position of a soccer ball when it has the greatest amount of gravitational potential energy?
C
Provide two examples of how you can increase the potential energy of a system.
increasing the height in a system increase gravitational potential energy
stretching a rubber band increases elastic potential energy
Amy uses 20N of force to push a lawn mower 10 meters. How much work does she do?
200 Joules
In a local competition, students race model cars that they built. The cars were held still at the top of a ramp and then released. Each car’s velocity was measured at the bottom of the ramp to calculate each car’s kinetic energy. Based on the data in the table, which of these could be the potential energy of Car 2 at the top of the hill?
A. 6 joules
B. 10 joules
C. 12 joules
D. 15 joules
What is the Kinetic Energy of a 100 kg object that is moving with a speed of 12.5 m/s?
7,812.5 J
Imagine Tony Hawk is absolutely shredding it at a skate park one day. He sends it straight into a half pipe and goes flying in the air. Describe the relative amounts of energy at the highest point of his jump.
At the highest point of his jump he will have the most gravitational potential energy and no kinetic energy
What is the difference between an energy transfer and energy transformation?
Adding or removing energy from a system is a energy transfer
When energy stays within a system but changes into a different form is an energy transformation
The diagram shows a cart moving freely along a track. What happens to the energy of the cart as it moves from point A to point B on the diagram?
A. Potential energy is transformed to kinetic energy.
B. Kinetic energy is transformed to potential energy.
C. Both potential energy and kinetic energy stay the same.
D. Potential energy decreases and kinetic energy stays the same.
A. This is correct because the cart has the largest amount of potential energy at point A at the top of the hill, and this energy is transformed to kinetic energy as it moves to point B at the bottom of the hill.
A carpenter leaves several tools on the floor of his workshop when he goes for his lunch break. Sometime later the carpenter returns and sees that one of his coworkers has moved his tools to different shelves on a nearby bookshelf.
Which data would the carpenter need to collect to calculate the amount of work required to lift his tools onto the shelves?
A. the height of each shelf
B. the time it took to move each tool
C. the amount of force needed to lift each tool
D. the strength of the person who moved the tools
A 70 kg man pushes a 30 kg stroller with a 10 kg child in it. The stroller is moving at a speed of 2.0 m/s. Calculate the combined kinetic energy of the child and the stroller.
80 J
What is the gravitational potential energy of a 2.5kg object that is 300m above the surface of the earth?
7,350 J
How can I increase the potential energy of two magnets with likes poles facing each other?
When two like poles of a magnet are facing each other they will repel. By moving the magnets closer together, the potential energy increases
An object has a gravitational potential energy that is 833 J. Its height above ground is 4.25 m. What is its mass?
20 kg
Provide 3 examples of kinetic energy and 3 examples of potential energy.
Kinetic: Thermal, electromagnetic, sound, electrical
Potential: Elastic, chemical, nuclear, magnetic
Two cars are driving down the road. Car A has a mass of 1100kg and is moving at 20m/s. Car B has a mass of 1000kg and is moving at 30m/s. Which car has more kinetic energy and why?
A. car A because it has more mass and almost the same speed as car B
B. car B because it has a greater speed and almost the same mass as car A
C. car A because it has a lower speed and almost the same mass as car B
D. car B because it has less mass and almost the same speed as car A
B. The speed has a greater effect on kinetic energy. Car A and Car B have similar masses, but Car B is traveling at a greater velocity. That difference in velocity causes Car B to have greater kinetic energy.
Consider these two pictures of an archer. Identify which picture models the greatest potential energy.
Describe the energy transformations that would occur if the archer were to release the bow string in each picture.
the picture with the string pulled back
Potential energy would be converted to kinetic energy in each picture, but in the first picture it would be just the gravitational potential energy because the arrow would fall straight down.
In the second picture, gravitational potential energy and elastic potential energy would be converted to kinetic energy because the arrow would fly forward and then also fall downward
A nuclear power plant captures the energy produced by the fission of the nuclei of uranium atoms and uses the generated energy to boil water. The boiled water produces steam that spins a series of turbines as it rises. As each turbine spins, it generates power that is sent into the power grid. Write one letter in each blank for the correct terms to describe the types of energy generated in a nuclear power plant. Some letters may be used more than once or not at all. The uranium atoms contain 1.__________ energy. The heat from their fission increases the 2.__________ energy of the water. The spinning of the turbines is 3.__________ energy that then generates 4.__________ energy used in people’s homes.
A. chemical B. electrical C. light D. kinetic E. nuclear F. thermal
1. Nuclear
2. Thermal
3. Kinetic
4. Electrical
Explain how the concepts of energy transformation and conservation of energy allow you to track how energy moves through a system.
Because energy is not created or destroyed, the total amount of energy in a system can be tracked by knowing the energy inputs and outputs of the system.The energy transformations can tell us the types of forms of energy in the system. In some cases the energy can escape.