Energy, Work, and Power Quiz

Energy, Work, and Power

• Work is the transfer of energy that occurs when a force makes an object move.
• Work is done if a force is applied and the object moves in the same direction as the force.
• The SI unit for work is Joules (J).
• Work done on a system depends only on forces and distances.
• Work = Force × Distance (W = Fd)
  • W = Work (Joules)
  • F = Force (Newtons)
  • d = Distance (meters)

Calculating Work

• Jessica applies a force of 2 N to move a book 1.5 m vertically.
• Work done on the book = 2 N × 1.5 m = 3 Joules
• While holding a book, Jessica moves it sideways with a force of 0.5 N for 0.5 meters.
• Work done on the book = 0.5 N × 0.5 m = 0.25 Joules

Power

• Power is the rate at which work is done.
• Power = Work / Time (P = W/t)
  • P = Power (Watts)
  • W = Work (Joules)
  • t = Time (seconds)
• The SI unit for power is Watts (W).
• Power is also measured in kilowatts (kW)
  • 1 kW = 1000 W
• A runner does 1,000 J of work in a time of 8 seconds at a power of 125 Watts.
• Jessica does 3 J of work in 2 seconds at a power of 1.5 Watts.

Energy

• Energy is the ability to cause change.
• Energy can change the object itself or its surroundings.
• Energy is measured in Joules (J).

Forms of Energy

• Some forms of energy include electromagnetic, chemical, nuclear, mechanical, and heat.
• Energy can change between these forms. (e.g., electrical energy transforming into thermal energy, light energy)

Electromagnetic Energy

• Power lines carry electromagnetic energy to homes as electricity.
• A potential energy difference causes electrons to flow.

Chemical Energy

• Chemical energy is stored in atoms' bonds.
• Chemical energy bonds atoms together and is released when bonds are broken.
• Fuel and food are forms of stored chemical energy.

Nuclear Energy

• The nucleus of an atom is the source of nuclear energy.
• When the nucleus splits (fission), nuclear energy is released as heat and light energy.
• Nuclear energy is also released when nuclei collide at high speeds and join (fusion).
• Nuclear energy is a concentrated form of energy (significant amount in a small space).

Mechanical Energy

• When work is done on an object, it acquires energy.
• This energy can be potential or kinetic.
• The combined energy is known as mechanical energy.
  • Throwing a bowling ball transfers mechanical energy to the ball.
  • Kicking a football transfers mechanical energy to the ball.
  • The internal motion of atoms is heat energy (or thermal energy) when moving particles produce heat.
  • Heat energy can be produced by friction.
  • Heat energy causes changes in temperature and phase of any form of matter.

Kinetic Energy

• Kinetic energy (KE) is the energy of motion.
  • KE = ½ mv²
• m = mass (kg)
• v = velocity (m/s)
• A 10-kg bowling ball rolling at 3 m/s has 45 Joules of kinetic energy.
• A ball rolling down a hill with a velocity of 4.5 m/s and mass of 3 kg has a kinetic energy of 30.375 Joules.

Potential Energy

• Potential energy (PE) is stored energy.
• Potential energy comes from an object's position.
  • Elastic PE
  • Electrical PE -Gravitational PE

Gravitational Potential Energy (GPE)

• GPE is energy stored in objects that can fall.
  • GPE = mgh
• m = mass (kg)
• g = acceleration due to gravity (9.8 m/s²)
• h = height (meters)
• A 0.5-kilogram slinky on a desk 1 meter above the floor has a GPE of 4.9 Joules.

Law of Conservation of Energy

• Energy is never created or destroyed, only transformed or transferred.
• The total amount of energy in a closed system never changes.

Transfer of Energy

• Energy can only transfer between forms, not be created or destroyed.
  • Kinetic and potential energy change as a ball rolls down a sloping surface.
  • The transfer of energy between a system and the environment results in an exchange of energy.

Transforming Energy

• Energy can change types - it can be transformed
• Energy in = Energy out (Energy is conserved)

Mechanical Energy

• Mechanical energy is the total amount of kinetic and potential energy in a system.
• System: a group of objects that work together.
• Mechanical Energy = Kinetic Energy + Potential Energy
  • ME = KE + PE
  • ME = ½ mv² + mgh

Example Problem (Mechanical Energy)

• A box has 15 Joules of potential energy and 32 Joules of kinetic energy.
  • The mechanical energy of the box is 47 Joules.

Example Problem (Mechanical Energy - Diving Board)

• A 75-kg person on a diving board 15 meters above the ground has a certain amount of mechanical energy (composed of GPE and KE).

Example Problem (Mechanical Energy - Falling Man)

• A falling man traveling at 9.9 m/s after falling 5 meters has a certain amount of mechanical energy.

Conservation of Energy (Loss of Mechanical Energy)

• Mechanical energy can be lost due to work (e.g., friction).
• Friction produces heat, which takes energy.

Test your understanding of concepts related to energy, work, and power. This quiz covers the definitions, calculations, and units for work and power in physics. Prepare to apply these concepts in practical scenarios and solve related problems.