Conservation of energy (Extended Response)

Question 1

Describe the energy transfers taking place during the motion of a simple pendulum over time.
Your answer should refer to the energy stores and energy transfers involved.

Answer 1

• the pendulum is first raised to a small angle
• gains gravitational potential energy
• when released the gpe transfers mainly to kinetic energy
• some energy will be lost as sound and heat by thermal transfer from friction due to air resistance
• conservation of energy states that the energy in a closed system always remains the same as energy cannot be created or destroyed
• energy started as all gpe
• mechanically transferred to ke once the pendulum starts to swing
• at the bottom of the swing the gpe is most/greatly reduced
• energy is mostly kinetic (or heat/sound)
• eventually the pendulum stops swinging
• gpe has transferred to ke but has all been lost through heat/air resistance or sound
• is now in the surroundings, which are slightly warmer
• useful energy store has dissipated to the surroundings

Question 2

The people on a small island want to use either wind power, on hills and out at sea, or its reserves of coal to generate electrical energy.

Compare the advantages and disadvantages of each resource.

Answer 2

wind:

• renewable so won’t run out/lasts indefinitely
• no fuel needed, so is very cheap to run
• no carbon dioxide emissions, so doesn’t contribute to the greenhouse effect/global warming
• unsightly, so is unpleasant to look at
• unreliable, only works in certain conditions so could fail if there is a lack of wind

coal:

• efficient, generates a lot of energy using a small amount
• reliable, the output doesn’t change depending on certain conditions
• non renewable, will eventually run out
• emits CO2, CO2 is a greenhouse gas which contributes to global warming
• emits sulfur dioxide, which can cause acid rain