Heat, Machines and Energy Transfer

How heat moves by conduction, convection and radiation, specific heat capacity, and simple machines as force or distance multipliers.

17 questions, free, marked as you go with a worked explanation on every one.

What this covers

The questions

  1. A metal spoon left in a pot of hot soup becomes hot along its whole length. Which method of thermal energy transfer is mainly responsible?
  2. How much thermal energy is needed to raise the temperature of 250 g of water by 30 °C? Water has a specific heat capacity of 4.19 J/(g·°C). Give your answer in joules.
  3. Why does Vancouver have milder winters than Calgary, despite being at a similar latitude?
  4. A worker pushes a crate 3.5 m along the floor with a steady force of 200 N in the direction of motion. How much work is done, in joules?
  5. A lever is used to lift a 600 N load with an effort of just 150 N. What is the mechanical advantage of the lever?
  6. A machine is supplied with 875 J of energy and does 700 J of useful work. What is its percent efficiency?
  7. According to the particle model of matter, what happens to the particles in a metal bar as it is heated?
  8. A house loses 4 500 J of thermal energy each second through poorly insulated walls. Adding insulation cuts that loss by 60%. How many joules per second are lost afterwards?
  9. Use the table. Which method of heat transfer explains feeling the Sun's warmth from a distance, with nothing physical in between?
  10. How much thermal energy is released when 100 g of water cools by 20°C? Water has a specific heat capacity of 4.19 J/(g·°C). Give your answer in joules.
  11. Heat moves through a solid metal rod mainly by which method?
  12. A 50 g metal block absorbs 2 370 J of thermal energy and its temperature rises from 20°C to 70°C. What is its specific heat capacity, in J/(g·°C)?
  13. A vacuum flask has an empty gap between its inner and outer walls. This gap is designed to block which method of heat transfer, which normally needs a material to travel through?
  14. A light bulb is supplied with 60 J of electrical energy and produces 12 J of light energy, with the rest lost as heat. What is its percent efficiency?
  15. An electric kettle takes in 1500 J and delivers 1275 J of useful heat to the water. What is its percent efficiency?
  16. Where does most of the energy lost by an inefficient machine usually go?
  17. A motor is 75 percent efficient and is supplied with 400 J of energy. How much useful energy does it deliver, in joules?

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