Units (Astrophysics)
3 marks · NormalA moon has a mass of 7.3 × 10^22 kg. It is in orbit around its planet.
State the SI unit for mass.
Explain why the gravitational force between the moon and its planet is much greater than the force between two footballs of similar size.
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) kilogram (kg)
(b) The moon and its planet have much larger masses than footballs. Gravitational force depends on the product of the two masses, so much greater masses mean a much greater force between them than between two footballs.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Mass unit given as kilogram (kg).
B2 (b) · 1 mark · Recognises that planets/moons have much larger mass than footballs.
B3 (b) · 1 mark · Links strength of gravitational force to mass (force ∝ mass × mass).
Worked solution
a. The SI unit for mass is kilogram (kg). b. The gravitational force between two objects depends on their masses. The moon and its planet have huge masses compared to two footballs, so the force between them is much greater.