Work Energy Power

A toy robot runs on batteries and is operated by a remote control. The robot is made to walk in a circle and then talk. What type of energy transformations occur during this process?

• kinetic energy to heat energy to sound energy

• nuclear energy to kinetic energy to sound energy

• thermal energy to potential energy to sound energy

• chemical potential energy to kinetic energy to sound energy

The diagram below illustrates a ball rolling down a hill at four different points. The ball at point A has 100 Joules of potential energy. As the ball rolls down the hill, what is the first illustrated point at which the kinetic energy would be greater than the potential energy?

• A

• B

• C

• D

A child pulls a toy car along a smooth, frictionless concrete floor. The forces in newtons (N) and distances in meters (m) are shown in the graph below. Based on the information in the graph, which of the following represents the correct amount of work in joules (J) to pull the car 8m?

• 3 J

• 32 J

• 192 J

• 16 J

Emilia walks out of her classroom into the bright sunshine. She glances at the hot sun as she touches the cement wall of her classroom. The cement wall feels very warm when she touches it. Which of the following sequences correctly describes the transfer of the sun’s energy to Emilia’s finger?

• potential energy to electrical energy to light energy to heat energy

• nuclear energy to electromagnetic energy to heat energy to kinetic energy

• nuclear energy to electromagnetic energy to kinetic energy to thermal energy

• potential energy to heat energy to kinetic energy to electromagnetic energy

“The amount of chemical energy in a flashlight’s battery is equal to the radiant energy transferred to the environment.” Is this statement correct?

• Yes, flashlights are 100% efficient at transferring the chemical energy of the battery into radiant energy.

• No, all energy transformations are inefficient. Some of the chemical energy will be lost as thermal energy.

• No, the Law of Conservation of Energy does not apply to this situation because the system is not a closed.

• Yes, the Law of Conservation of Energy states that the total energy in a system can never be created or destroyed.

A group of four students are researching a question about the transformation of energy that occurs when a tennis ball is dropped from a height of 1.5 m. They observe and measure the first rebound height, then let the ball continue to fall and again observe and measure the second rebound height before catching the ball. Their measurements show the tennis ball's rebound height decreasing each

time the ball bounced. As they analyze their results, they discuss the changes in energy. Which one of the following students has the correct statement about the energy transformations?

• Alyssa said, "The maximum gravitational potential energy changed into the minimum kinetic energy during the first drop. That is why the ball doesn't bounce up the same height."

• Bryan said, "The maximum gravitational potential energy changed into the minimum kinetic energy during the first drop down. Energy cannot be created or destroyed so we must have made a mistake in our procedure. That is why the ball doesn't bounce up the same height."

• Christopher said, "The maximum gravitational potential energy changed into the maximum kinetic energy during the first drop. The energy then changed into sound before it rebounded and bounce

  back up. I heard the ball bounce, that is why the ball doesn't bounce up the same height."

• Dawn said, "The maximum gravitational potential energy changed into the maximum kinetic energy during the first drop of the ball. The energy then changed into heat and sound before it rebounded and bounced back up. That is why the ball doesn't bounce up the same height."

Two elevators in a hotel are being used to transport guests. Elevator A is moving a force of 3000 N a distance of 10 meters in 10 seconds. Elevator B is moving a force of 6000 N a distance of 10 meters in 20 seconds. Which of the following statements correctly compares the work and power of the

elevators?

• Elevator A develops more power than Elevator B.

• Elevator A does more work than Elevator B.

• Elevator B develops more power than Elevator A.

• Elevator B does more work than Elevator A.

Jamie is loading four family suitcases into a car's trunk. The height from the ground to the trunk of the car is 0.70 m. Consider the amount of power needed to lift the following four suitcases. How would you rank the suitcases from the greatest amount of power to the least amount of power needed to lift each suitcase into the car's trunk?

First - 150 N was lifted in 1.5 seconds

Second - 200 N was lifted in 1.8 seconds

Third- 210 N was lifted in 2.0 seconds

Fourth - 220 N was lifted in 2.3 seconds

• first, second, third, and fourth

• second, third, first, and fourth

• fourth, first, third, and second

• fourth, third, second, and first

A drama teacher purchases a motor that can lift an 1800-Newton curtain a distance of 10 meters in exactly 5 seconds. Which of the motors described below did the drama teacher buy, and how much work will the motor do as it lifts the curtain?

• motor A, which has a power rating of 0.9 kW and does 9 kJ of work

• motor B, which has a power rating of 0.9 kW and does 18 kJ of work

• motor C, which has a power rating of 3.6 kW and does 9 kJ of work

• motor D, which has a power rating of 3.6 kW and does 18 kJ of work

The graph shows work done versus time for a robotic arm performing a three-second task in an assembly line.

At what time is the robotic arm using the most power?

• just after 0 s

• just before 1 s

• just after 2.5 s

• just before 3 s