Work Energy Power Facts Review

What are the units for energy?

• Watts (s)

• Joules (J)

• Radians (rad)

• Watts per Second (W/s)

Answer explanation

All forms of energy have units of joules, abbreviated J.

What are the units for work?

• Watts (s)

• Joules (J)

• Radians (rad)

• Watts per Second (W/s)

Answer explanation

All forms of energy have units of joules, abbreviated J.

What are the units for power?

• Watts (s)

• Joules (J)

• Radians (rad)

• Watts per Second (W/s)

Answer explanation

The units of power are joules per second, which are also written as watts.

Which of the following corresponds to kinetic energy?

• mgh

• "sum of kinetic and potential energy"

• ½kx²

• heat energy that causes an increase in the temperature of the system

Answer explanation

Kinetic energy: KE = ½mv².  Here, m is the mass of the object, and v is its speed.

Which of the following corresponds to gravitational potential energy?

• mgh

• "sum of kinetic and potential energy"

• ½kx²

• "heat energy that causes an increase in the temperature of the system"

Answer explanation

Gravitational potential energy: PE = mgh.  Here, m is the mass of the object, g is the gravitational field, and h is the vertical height of the object above its lowest position.

Tags

NGSS.HS-PS3-2

Which of the following corresponds to internal energy?

• mgh

• "sum of kinetic and potential energy"

• ½kx²

• "heat energy that causes an increase in the temperature of the system"

Answer explanation

Internal energy is heat energy that causes an increase in the temperature of the system.

Tags

NGSS.HS-PS3-4

Which of the following corresponds to spring potential energy?

• mgh

• "sum of kinetic and potential energy"

• ½kx²

• "heat energy that causes an increase in the temperature of the system"

Answer explanation

Spring potential energy: PE = ½kx².  Here, k is the spring constant, and x is the distance the spring is stretched or compressed from its equilibrium position.  (See the section below about springs)

Tags

NGSS.HS-PS3-2

Which of the following corresponds to mechanical energy? Select the best option.

• mgh

• "sum of kinetic and potential energy"

• ½kx²

• "heat energy that causes an increase in the temperature of the system"

Answer explanation

The term mechanical energy refers to the sum of a system’s kinetic and potential energy.

How should EVERY energy problem be started?

• W=FD

• define the system and draw an annotated bar chart

• Relevant equation for KE, GPE, or SPE

• Friction Equation

Answer explanation

Work-energy theorem

1. Define the object or system being described.

2. Draw an annotated energy bar chart.

3. Write an equation using the energy bar chart: bars + bars = bars. 

Work-energy theorem

1. Define the object or system being described.

2. Draw an annotated energy bar chart.

3. Write an equation using the energy bar chart: bars + bars = bars. 

Using bars + bars = bars, which of the following statements are true (select TWO answers)?

3 + 3 - 2 = 1 + 3

• The energy of the system increases

• The energy of the system decreases

• Work is directed parallel to the direction of motion

• Work is directed antiparallel to the direction of motion.

Answer explanation

Work-energy theorem

1. Define the object or system being described.

2. Draw an annotated energy bar chart.

3. Write an equation using the energy bar chart: bars + bars = bars. 

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-2