lunch box insulation material temperature after 30 min / degrees C A none 46 B foam 58 C foil-lined foam 61 D vacuum wall 68 This apparatus is used to test ...
Question 1 Report
| lunch box | insulation material | temperature after 30 min / degrees C |
|---|---|---|
| A | none | 46 |
| B | foam | 58 |
| C | foil-lined foam | 61 |
| D | vacuum wall | 68 |
This apparatus is used to test a toy launcher. Fig. 1 shows a spring compressed by 4.0 cm before it pushes a small cart along a track. The cart then climbs a ramp and stops at point P. Friction between the cart wheels and the track is small but not zero. The students repeat the test using the same cart and a greater compression.
(a) What energy store increases when the spring is compressed? [1]
(b) Describe the main energy transfers as the cart moves up the ramp. [2]
(c) Which position gives the cart its greatest gravitational potential energy? [1]
The table below gives the temperature inside four identical lunch boxes after they have been outdoors for 30 minutes. Each box begins with soup at 75 degrees C. Box D has a vacuum layer between two walls. The students use the results to compare how well each design reduces energy transfer to cold air.
| lunch box | insulation material | temperature after 30 min / degrees C |
|---|---|---|
| A | none | 46 |
| B | foam | 58 |
| C | foil-lined foam | 61 |
| D | vacuum wall | 68 |
(a) Which lunch box has the smallest temperature decrease? [1]
(b) Calculate the temperature decrease for box C. [1]
(c) Describe how foam reduces energy transfer by conduction. [2]
(d) Explain why a vacuum layer reduces conduction and convection. [1]
Answer Details
Spring launcher
- (a) Compressing the spring increases its elastic potential energy store. [1]
- (b) The spring's elastic potential energy is transferred to the cart's kinetic energy store. [1] As the cart climbs, kinetic energy is transferred to its gravitational potential energy store. [1] A small amount is also dissipated by friction, but the question asks for the main transfers.
- (c) The cart has its greatest gravitational potential energy at point P, its highest position. [1]
Lunch boxes
- (a) Box D has the smallest temperature decrease: it finishes at 68 °C, the highest final temperature. [1]
- (b) \[ \text{temperature decrease}=75-61=14\ ^\circ\text{C} \] 14 °C. [1]
- (c) Foam contains trapped air. [1] Air is a poor conductor, so particles transfer energy slowly through the foam. [1]
- (d) A vacuum contains no particles, so there are no particles to conduct energy or to form convection currents. [1]
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