1.1 SI units, prefixes and converting units
9 exam questions worth 14 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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What is 2.4 km in metres?
Choose one answer.
Correct Not quite: the answer is 2400 m
Mark scheme
D: 2400 m
Model answer
2400 m (D), because 1 km = 1000 m.
Write 0.35 A as a current in milliamperes (mA).
Mark scheme
350 (mA)
Model answer
350 mA, because 1 A = 1000 mA.
Convert 2.5 hours into seconds.
Mark scheme
2.5 × 60 × 60 (1); 9000 (s) (1)
Model answer
2.5 × 60 = 150 minutes, then 150 × 60 = 9000 s.
Write 0.000 062 m in standard form.
Mark scheme
6.2 × 10-5 (m)
Model answer
6.2 × 10-5 m.
State the SI unit of mass.
Mark scheme
kilogram / kg do not accept gram
Model answer
The kilogram (kg).
A student measures a mass of 450 g and uses it in the equation for gravitational potential energy. Convert the mass into the unit that must be used in the equation, and explain why.
Mark scheme
0.45 kg (1); the SI unit of mass is the kilogram / equation only works with kg / unit of energy is the joule (1)
Model answer
450 g = 0.45 kg. The equation only gives an answer in joules if the mass is in kilograms, the SI unit of mass.
How many square centimetres (cm²) are there in one square metre (m²)?
Choose one answer.
Correct Not quite: the answer is 10 000
Mark scheme
C: 10 000
Model answer
10 000 (C). Both sides of the square are multiplied by 100, so the area is multiplied by 100 × 100.
Convert a speed of 108 km/h into m/s.
Mark scheme
108 ÷ 3.6 (1); 30 m/s (1)
Model answer
108 ÷ 3.6 = 30 m/s.
A student uses the equation for kinetic energy, E_k = \frac{1}{2} m v^2, for a ball of mass 600 g moving at 5.0 m/s. She gets an answer of 7500 J. Explain her mistake and calculate the correct value.
Mark scheme
she used the mass in grams, not kilograms (1); mass = 0.60 kg (1); E = ½ × 0.60 × 5.0² = 7.5 J (1)
Model answer
She used 600 for the mass, but it must be in kilograms (0.60 kg). The correct answer is ½ × 0.60 × 25 = 7.5 J.
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