Work and Energy Concepts Quiz

Work and Energy

• Work is done when energy is required
• Animals use food for energy
• Machines use fuel for energy
• Reading, writing, thinking, and analyzing consume energy, but no scientific work is done in these activities
• A man trying to push a wall does zero work as the wall is stationary
• A person standing still with a weighty object is stationary and does no work
• Work is done when a moving object stops, an object starts moving, the velocity of an object changes, or the shape of an object changes
• Work occurs when a force is applied to a body and that force causes motion
• For work to be done, a force must be applied to a body, and the body must be displaced

Condition of Work Done

• Force must be applied to the body
• Body must be displaced

Work is Done When

• A cyclist is pedaling a cycle
• A person is lifting a load upwards or downwards

Work is Not Done When

• A coolie carries a load and stands stationary
• A person applies force on a big rock

Work Done by a Fixed Force

• Work done in moving a body equals the product of force and displacement in the direction of force
• Work = Force × Displacement
  • W = F × S
• Work is a scalar quantity

Units of Work

• Newton metre or Joule
• A force of 1 Newton moves a body 1 metre in its direction; the work done is 1 Joule
• 1 Joule = 1 Newton × 1 metre
• 1 J = 1 Nm

Work Done Against Gravity

• Work done against gravity equals the weight of the body multiplied by the vertical distance
• W = Weight × Vertical Distance
  • W = m × g × h
    • Where:
      • m = mass of the body
      • g = acceleration due to gravity
      • h = height the body is lifted

Factors Affecting Work Done

• Magnitude of force
  • Greater the displacement, the greater the work done (and vise-versa)
• Displacement
  • Greater the displacement, the greater the work done (and vise-versa)

Negative, Positive, and Zero Work

• Positive work: Force acts in the direction of the body's motion (e.g., a child pushing a toy car)
• Negative work: Force acts opposite to the body's direction (e.g., friction slowing a moving ball)
• Zero work: Force acts at right angles to the direction of motion (e.g., the moon orbiting Earth)

Energy

• The capacity to do work is known as energy
• The sun is the primary source of energy
• Energy from the sun fuels many processes
• Energy is derived from the sun
• Some energy is sourced from the Earth(tides)

Forms of Energy

• Mechanical energy: energy due to motion or position
• Kinetic energy: energy due to motion
  • Examples: a moving cricket ball, running water, a moving bullet, flowing wind, a moving car, a running athlete, a rolling stone, flying craft
• Potential energy: energy due to position or shape change
  • Examples: water dam, wound-up spring, bent string, etc.

Kinetic Energy Formula Derivation

• W = F × s
• W = ½ mv² - ½ mu²
• If ‘u’ (initial velocity) = 0, then W = ½ mv²
• Work done = Change in kinetic energy

Potential Energy

• Energy due to position or shape change
• Examples include height, stretching, twisting, bending

Transformation of Energy

• Changing one form of energy into another form is known as energy transformation
• Example: a stone at a high position has potential energy. When it falls, potential energy is converted into kinetic energy and maximum kinetic energy is achieved when the stone hits the ground
• Potential energy is transformed into kinetic energy

Laws of Conservation of Energy

• Energy conversion occurs where the total energy remains constant
• Energy neither created nor destroyed

Rate of Doing Work - Power

• Power is the rate of energy consumption
• Power = Work done/Time taken

Units of Power

• SI unit of power is Watt (W)
  • 1 Watt = 1 Joule / 1 second
• Numericals need practice.

Average Power

• Average Power = Total work done/ Total time taken

Commercial Unit of Energy

• Joule is inconvenient for large quantities of energy
• Kilo-watt-hour (kWh) is a more practical unit
• 1 kWh = 1 kilowatt × 1 hour
  • 1 kWh = 3.6 × 10⁶ J

Test your understanding of the concepts of work and energy in this engaging quiz. Explore situations where work is done and where it is not, and learn how force and motion are related. Perfect for students looking to reinforce their knowledge in physics.