Chapter 4: Energy
How is power calculated?
Power = energy converted divided by the time it takes to convert it.
Which friction converts KE to TE more than the other: sliding or static?
Sliding friction does since there is motion involved. Static friction only exists when something is at rest.
What is unique about gravitational potential energy?
Stored energy that is based on the mass & height of the object.
If a roller coaster has 300, 000 Joules of GPE at the top of a hill, how much KE does it have when it is halfway down (ignoring friction)?
150,000 Joules
On what does potential energy depend?
Amount of stored energy to be used later
What type of energy is held by a compressed bouncy ball and a stretched bow?
Elastic potential energy
What is unique about elastic potential energy?
Energy that is stored in a flexible object.
What is unique about chemical potential energy?
Energy that is stored in chemical bonds.
How is the stored energy different in fats, carbohydrates, and proteins?
Fats have 9 calories per gram Carbohydrates have 4 calories per gram Proteins have 4 calories per gram
Why does a bouncy ball have less and less ME after each bounce?
Friction converts some energy into thermal energy that cannot be used again.
How does increasing the speed of an object affect its PE?
It does not affect the potential energy; mass & height affect potential energy.
How does increasing mass affect GPE?
It increases the Gravitational Potential Energy
What happens to the GPE of an object as it falls?
It is converted to kinetic energy.
What is meant by work?
It is movement of an object as a result of an applied force. Energy is required to do this task.
What is meant by power?
It is the rate at which energy is transformed, measured in watts. A 60W bulb converts electrical energy into thermal energy & light twice as fast as a 30W bulb.
What is unique about mechanical energy?
It is the sum of kinetic energy & potential energy, not including thermal energy. It can be used again which is why thermal energy is not part of mechanical energy.
What happens to water in a hydroelectric station?
Its gravitational potential energy gets converted to kinetic energy, then its kinetic energy gets converted into electrical energy.
What are the typical units of energy?
Joules
Describe the NRG conversions in a car.
The engine converts chemical potential energy in the gasoline into kinetic, which is the motion of the car.
How is mechanical energy defined?
The sum of kinetic energy & potential energy, excluding thermal energy
How do plants have stored up CPE?
They got light energy from the sun in photosynthesis, changing it into stored chemical potential energy. When we eat plants, we convert that chemical potential energy into kinetic energy.
What are the typical units of power?
Watts
Does energy have to involve motion?
Yes, if it is kinetic energy. No, if it is stored potential energy.
