A pure liquid cools at a steady rate of energy loss. Its temperature falls from 60 °C to 40 °C in 4 minutes, stays at 40 °C for 6 minutes, then falls below 40 °C.
024681012203040506070Time (min)Temperature (°C)
.1
Calculate the average rate of temperature decrease during the first 4 minutes, in °C per minute.
[2 marks]
.2
Explain the horizontal section and the fall afterwards on the temperature-time graph.
[3 marks]
7 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
A spring stores 0.72 J when compressed by 0.060 m. It obeys Hooke's law throughout this compression. It launches an initially stationary 0.090 kg toy horizontally; 25% of the stored energy is dissipated.
.1
Calculate the spring constant.
[2 marks]
.2
Calculate the toy's speed when it leaves the spring.
[3 marks]
.3
Explain why the speed cannot be found by treating the dissipated energy as destroyed.
[2 marks]
4 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
A 12 V battery is connected to two identical fixed resistors in series. A voltmeter across one reads 6.0 V. The resistors are then connected in parallel across the same ideal battery; their resistances do not change.
Compare the voltage across each resistor, the current in each resistor and the total battery current in the two arrangements.
[4 marks]
6 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
At fixed potential difference 3.0 V, a thermistor carries 0.0020 A in cool water and 0.0060 A in warm water. It is the type whose resistance falls as temperature rises.
.1
Calculate the resistance in cool water.
[2 marks]
.2
Calculate the resistance in warm water.
[2 marks]
.3
A pupil says the current tripled because the supply voltage tripled. Evaluate the statement using the data.
[2 marks]
4 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
Two identical bar magnets are placed with their north poles facing one another across a small gap. A field sensor is moved along the line between the poles.
.1
Explain why the field can be very weak at the midpoint even though each magnet separately has a strong field there.
[2 marks]
.2
Explain the force between the magnets and how the result differs if one magnet is reversed.
