Science Grade 8 Unit 2 Assessment

Front

How is energy transferred by radiation?

Back

through electromagnetic waves

Answer explanation

Energy is transferred by radiation through electromagnetic waves, such as light and heat. This process does not require a medium, unlike conduction or convection, making it unique in how energy can travel through space.

Front

A student holds an ice cube in his hand to demonstrate the transfer of thermal energy. In his hand, the ice cubes quickly begin to melt. Which BEST describes the process of thermal energy the student is demonstrating?

Back

Conduction, where heat is transferred from his hand to the ice cubes. The warm hand transfers thermal energy to the ice cubes through conduction, causing the ice to melt.

Answer explanation

The correct choice is B. The student demonstrates conduction as his warm hand transfers thermal energy to the ice cubes, causing them to melt and undergo a phase change into liquid.

Front

According to the law of conservation of energy, what happens to mechanical energy if it is not used to move an object?

Back

It is converted into another form of energy.

Answer explanation

According to the law of conservation of energy, mechanical energy that is not used to move an object is converted into another form of energy, ensuring that energy is neither created nor destroyed.

Front

What energy transformations occur that enable him to bake cookies?

Back

light energy → electrical energy → heat energy

Answer explanation

To bake cookies, light energy is converted into electrical energy (from the oven), which then transforms into heat energy to bake the cookies. Thus, the correct transformation is B: light energy → electrical energy → heat energy.

Front

Give an example for each form of energy: light, heat, sound, electrical, mechanical.

Back

light: turns on a lamp, heat: makes toast, sound: listens to the radio, electrical: plugs in coffee pot, mechanical: rides her bike

Answer explanation

Choice C correctly matches each form of energy to Jennifer's actions: light for turning on a lamp, heat for making toast, sound for listening to the radio, electrical for plugging in the coffee pot, and mechanical for riding her bike.

Front

How does the ball's potential and kinetic energy change as it rolls down the hill?

Back

The ball's potential energy decreases, and its kinetic energy increases.

Answer explanation

As the ball rolls down the hill, it loses height, which decreases its potential energy. Simultaneously, it gains speed, resulting in an increase in kinetic energy. Thus, potential energy decreases while kinetic energy increases.

Front

At which point in a pendulum system does the pendulum bob demonstrate minimum potential energy?

Back

Point 2: The pendulum bob is at the lowest height, signifying the lowest potential energy.

Answer explanation

B. 2 is correct because the pendulum bob is at its lowest point, where potential energy is minimized. At this position, all energy is converted to kinetic energy, making potential energy the lowest.

Front

Where on the track is the total energy of the system the highest?

Back

The system has the most energy at R, S, and T because energy cannot be created or destroyed, so the total energy remains constant.

Answer explanation

The total energy of the system remains constant at points R, S, and T, as energy cannot be created or destroyed. Thus, the correct choice is that the system has the most energy at R, S, and T.

Front

How does thermal energy move from place to place?

Back

radiation, convection, and conduction

Answer explanation

Energy moves through radiation (transfer via electromagnetic waves), convection (transfer through fluid movement), and conduction (transfer through direct contact). Thus, the correct answer is radiation, convection, and conduction.

Front

A student wants to demonstrate the transfer of thermal energy. If she puts her warm hand on a cold metal doorknob, how will thermal energy move?

Back

Heat will move from her hand to the doorknob.

Answer explanation

Heat moves from her hand to the doorknob because thermal energy transfers from warmer objects to cooler ones. Her warm hand loses heat, making the doorknob feel cold.