If a machine has an efficiency of 80% and it does 400 J of useful work, how much

Practice Questions

Q1
If a machine has an efficiency of 80% and it does 400 J of useful work, how much energy was supplied to the machine? (2023)
  1. 500 J
  2. 400 J
  3. 320 J
  4. 600 J

Questions & Step-by-Step Solutions

If a machine has an efficiency of 80% and it does 400 J of useful work, how much energy was supplied to the machine? (2023)
  • Step 1: Understand that efficiency is a measure of how much useful work a machine can do compared to the total energy it uses.
  • Step 2: Write down the formula for efficiency: Efficiency = Useful Work / Total Energy Input.
  • Step 3: Rearrange the formula to find Total Energy Input: Total Energy Input = Useful Work / Efficiency.
  • Step 4: Plug in the values: Useful Work is 400 J and Efficiency is 80%, which is 0.8 in decimal form.
  • Step 5: Calculate Total Energy Input: Total Energy Input = 400 J / 0.8.
  • Step 6: Perform the division: 400 J divided by 0.8 equals 500 J.
  • Step 7: Conclude that the total energy supplied to the machine is 500 J.
  • Efficiency – Efficiency is the ratio of useful work output to the total energy input, often expressed as a percentage.
  • Energy Calculation – Understanding how to manipulate the efficiency formula to find total energy input based on given useful work and efficiency.
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