Unit 3 Review

In which of the following scenarios would this energy transformation be observed?

chemical → light → heat

• Starting a car

• Plucking a guitar string

• Turning on a fan

• Lighting a match

A gasoline-powered generator is used to provide lighting for a house.

• Electrical energy, generated as the electrons move through the wire, changes to chemical energy as the gasoline is burned. The chemical energy changes to mechanical energy from the generator which then changes to light energy seen from the light bulb.

• Thermal energy from friction between moving parts in the generator changes to mechanical energy from the generator. The mechanical energy is changed to chemical energy as the gasoline is burned and is changed to the light energy seen from the light bulb

• Mechanical energy from the generator changes to chemical energy from friction between the moving parts in the generator. This chemical energy changes to electrical energy as the electrons move through the wire and is changed to light energy seen from the light bulb.

• Chemical energy within the gasoline changes to mechanical energy as the generator's parts begin to move. The mechanical energy is changed to electrical energy, generated as the electrons move through the wire, and changes to to light energy seen from the light bulb

When energy enters a system and then comes out of the system later, the law of conservation of energy states that–

• the form of energy that comes out of the system must be the same form that entered

• the energy will always create a change in the properties of the parts of the system

• some of the energy that entered the system will remain in the system.

• the amount of energy coming out of the system must equal the energy that entered the system.

A student mixes yeast and baking soda to use in a volcano model. The mixture causes the volcano model to feel cool when it is touched. Which argument explains the energy transformations that have taken place?

• light energy changed to heat energy causing the temperature to increase making the volcano feel cool

• heat energy changed to chemical energy which caused a decrease in the temperature making the volcano feel cool

• chemical energy changed to heat energy which was absorbed from the volcano making it feel cool.

• chemical energy changed to light energy which draws heat from the volcano making it feel cool

The picture below shows a light bulb attached to a hand generator. Turning the handle makes a current that causes the light bulb to glow. What are the energy transformations that happen in this hand generator?

• Thermal → solar → light

• Solar → light → electrical

• Mechanical → electrical → light

• Electrical → mechanical → light

The image below shows the basic construction of a hydroelectric dam. A student claims that the type of energy transformation that occurs in this system is mechanical to electrical. Which of the following statements would BEST support the student's claim?

• Electricity must move to travel through power lines and reach people’s homes.

• The turbine must turn for electricity to flow from the generator to the power lines

• Water must flow from a higher place to a lower one for electricity to be created.

• The electricity flowing through the power lines has enough energy to move objects

An electric pencil sharpener uses electricity to make its motor spin. The pencil sharpener also makes noise and heats up. Which observation of the pencil sharpener demonstrates the law of conservation of energy?

• The amount of energy used by the electric pencil sharpener is greater than an electric lamp

• The amount of electrical energy used equals the total amount of mechanical, sound, and thermal energy produced.

• The electric pencil sharpener only uses energy when it is being used to sharpen a pencil

• The electric pencil sharpener is easier to use than the older version that was cranked by hand.

A graph showing the kinetic energy and mass of objects traveling at 10 m/s is shown below. An object traveling at 10 m/s has about 1,700 kilojoules of kinetic energy. What is the approximate mass of the object?

• 20–30 kg

• 30–40 kg

A ball is thrown into the air, as shown below.

At what point does it have the MOST stored energy?

• Point A – before it is thrown

• Point D – after it hits the ground

A picture frame sitting on a counter has potential energy because of the gravitational pull of Earth. Which of the following would increase the potential energy of the picture frame?

• Lifting it to a high shelf

• Dropping it on the floor