Energy

Which of the following statements is true about an open system and a closed system in the Law of Conservation of Energy?

• A. An open system and a closed system exchange matter and energy.

• B. An open system exchanges energy and closed system exchanges matter.

• C. An open system exchanges matter and a closed system exchanges energy.

• D. An open system exchanges matter and energy and a closed system exchanges energy.

Which of the following is an advantage for an open system?

• A. An open system is impermeable to radiation.

• B. An open system has a virtually unlimited supply of matter.

• C. An open system has a virtually unlimited supply of energy.

• D. An open system can prevent the influence of all external energy and matter.

Jeremiah is cooking rice on the stove in a pot that has a lid on it. Which of the following statements best describes the rice and pot?

• A. It is an open system because matter and energy are able to be transferred.

• B. It is a closed system because matter and energy are able to be transferred.

• C. It is an open system because energy can be transferred but matter can not be transferred.

• D. It is a closed system because energy can be transferred, but matter can not be transferred.

A skateboarder starts at the top of a long, steep incline. As he skates down the incline, he frequently angles the wheels to decelerate. Which option best describes the energy of the system consisting of the skateboarder, his skateboard, and the incline?

• A. Mechanical energy is conserved; kinetic energy is transformed into thermal energy.

• B. Mechanical energy is conserved; potential energy is transformed into kinetic energy.

• C. Mechanical energy is not conserved; kinetic energy is transformed into potential energy.

• D. Mechanical energy is not conserved; potential energy is transformed into thermal energy.

Paola was going on a picnic and decided she wanted to bring a cold beverage with her. She poured ice-cold lemonade into a thermos and placed the lid tightly on the thermos. When she was ready to drink her lemonade an hour later, the lemonade was still cold. Which of the following statements best describes why the lemonade remained cold?

• A. The thermos is an open system, in which matter and energy were able to escape.

• B. The thermos is an isolated system, in which matter and energy were able to escape.

• C. The thermos is an open system, in which neither matter nor energy were able to escape.

• D. The thermos is an isolated system, in which neither matter nor energy were able to escape.

Students were asked to compare open and closed systems. Four student responses are shown below.

Which student best described both a closed and an open system?

• A. student 1

• B. student 2

• C. student 3

• D. student 4

According to the Law of Conservation of Energy, which statement is true?

• A. There is a fixed amount of electrical energy in the universe.

• B. A solar-powered flashlight creates energy when it is operated.

• C. When a log is burned on a campfire, the potential energy stored inside the wood is destroyed.

• D. When a boy claps his hands, the kinetic energy of his hands is transferred into thermal and sound

  energy.

For a class presentation of a science project applying the Law of Conservation of Energy, a student plans to use a diagram of a wind turbine while explaining the transfer of energies to produce electricity. The following information is from the research:

I. Notes:

A computer moves the control unit so the turbine blades are always facing into the wind. A shaft is a long, narrow pole or rod that joins moving parts in a mechanical system.

II. Information about the turbine

Wind turbines are used in several states throughout the United States to generate electricity without burning fossil fuels. The turbine works from the horizontal motion of the wind when it spins the turbine’s blades and a rotor shaft. The spinning rotor shaft then rotates gears in a gearbox to increase the kinetic energy of the system. The increase in kinetic energy then spins the shaft that leaves the gearbox almost 50 times faster. The gearbox shaft converts the kinetic energy of rotation into electric energy inside the generator.

Which of the following titles would be best for this project?

• A. Wind Energy to Kinetic Energy in an Open System

• B. The Conservation of Electric Energy in an Open System

• C. The Conservation of Solar Energy in an Isolated System

• D. Heat Energy to Mechanical Energy in an Isolated System

Brian puts his bicycle on a stationary platform, and sets it up so that as he cycles, the motion recharges a pack of batteries. After an hour of cycling, he is tired. He leaves, eats lunch, and comes back to continue cycling. Which statement best describes this type of system?

• A. It is an open system because the meal provides energy to the system.

• B. It is an open system because energy is transferred to the batteries.

• C. It is a closed system because chemical energy crosses into and out of the system.

• D. It is a closed system because the energy transferred to the batteries comes from Brian.

A decorative water fountain is designed so that it may be installed even where there is no plumbing. Water is added once, and the water that falls from the top into a pool at the bottom is pumped back to the top again. The pump is electrical.

Which type of system best describes the water pump?

• A. open system, because energy is added to the system

• B. closed system, because energy is added to the system

• C. open system, because the water is recycled within the system

• D. isolated system, because the water is recycled within the system