Units (Forces and Motion)
3 marks · HardA scientist measures a force of 57 millinewtons (mN) using a digital force meter.
Convert this force reading into newtons (N), using the correct unit symbol.
If this force is applied to an object with a mass of 70 grams, calculate the acceleration produced (to 2 decimal places). Write your answer with the correct SI units.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 0.057 N · must show N
(b) 0.81 m/s² · must show m/s²
Must show: N, m/s²
Common mistakes: using incorrect factor for mN to N; not converting grams to kg
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct conversion from mN to N with unit and symbol.
M1 (b) · 1 mark · Uses F = ma, mass correctly converted to kg, substitutes values.
A1 (b) · 1 mark · Final answer to 2 d.p. and correct SI unit m/s².
Worked solution
a) 57 mN = 57 × 10⁻³ N = 0.057 N
b) Mass = 70 g = 0.070 kg. F = ma, so a = F / m = 0.057 N / 0.070 kg = 0.814 ≈ 0.81 m/s².