A designer tests a spring door closer in a library. Fig. 1 shows the door held open. A spring inside the closer is twisted when the door is opened. When rel...
Question 1 Report
A designer tests a spring door closer in a library. Fig. 1 shows the door held open. A spring inside the closer is twisted when the door is opened. When released, the door returns slowly to the frame. The closer is filled with oil, so the door does not slam. The designer wants the system to be safe while avoiding excessive sound and heating.
(a) Name the energy store that increases as the door is opened. [1]
(b) Explain how the oil helps prevent the door from slamming. [2]
(c) Give two unwanted energy transfers as the door closes. [2]
Fig. 1 shows a technician testing a solar cooker made from a reflective dish. Light from the sun is focused onto a black cooking pot. The pot contains 0.80 kg of water. During a test, the water temperature rises by 15 degrees C. The specific heat capacity of water is 4200 J/kg degrees C. The technician wants to compare the useful energy gain of the water with energy arriving from the sun.
(a) Name the useful energy store that increases in the water. [1]
(b) Calculate the energy gained by the water. [2]
(c) Give two reasons why not all of the light energy from the sun becomes useful energy in the water. [2]
Answer Details
Spring door closer
- (a) Opening the door increases the elastic potential energy store of the spring. [1]
- (b) The oil provides resistance to motion. Energy is dissipated and the door has a lower velocity, preventing it from slamming. [2]
- (c) Two unwanted transfers include heating of the oil, heating of the door/frame, and sound to the surroundings. [2]
Solar cooker
- (a) The water’s thermal/internal energy store increases. [1]
- (b) \[E=mc\Delta T=0.80\text{ kg}\times4200\text{ J/kg degrees C}\times15\text{ degrees C}=50400\text{ J}\] [2]
- (c) Any two: some light is reflected away; the dish or pot heats up; energy heats the surrounding air; or energy is transferred by evaporation. [2]
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