Astrophysics
5 marks · NormalThe surface gravity on Mars is different from that on Earth. Astronomers also classify stars based on their colour and temperature.
State the unit of gravitational field strength, and then use it to write the weight formula for an object of mass on a planet with gravitational field strength .
If a robot has a mass of 150 kg, calculate its weight on Mars where the gravitational field strength is 4 N/kg.
A scientist observes several stars. One is blue and another is red. Explain which has the higher surface temperature and why, based on the classification of stars by colour.
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(a) N/kg. Weight = mass × gravitational field strength, so W = m × g
(b) 600 N
(c) The blue star has a higher surface temperature because blue stars are hotter, while red stars are cooler. Colour indicates temperature.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct unit for gravitational field strength (N/kg)
M1 (a) · 1 mark · Correct weight formula given (W = m x g)
A1 (b) · 1 mark · Correct calculation of weight (600 N, with unit)
B2 (c) · 1 mark · States blue stars are hotter than red stars
E1 (c) · 1 mark · Links colour with temperature correctly (explanation)
Worked solution
a) The unit of gravitational field strength is newton per kilogram (N/kg). The formula for weight is:
b) For a mass of 150 kg and g = 4 N/kg:
c) Blue stars have a higher surface temperature than red stars. The colour of a star is related to its temperature: blue is the hottest, then white/yellow, then red as the coolest.