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Questions on the Earth in Space
Q17.

A writer of science fiction likes to make her stories as realistic as possible. In her latest book there is a group of space travellers who discover a star in a distant part of the galaxy. The travellers are excited to find a planet very similar to Earth orbiting this star. They call the planet Delta. The table compares data about Delta and the Earth. Most of the figures are relative.

 
Delta
Earth

The planet's distance from the star it orbits.

We know from this that the planet's year will be longer than Earth's. The further out the planet is the longer it takes to orbit the star.
1.5
1

Mass of the planet

Delta's mass is greater - but the density is the same! Density = mass/volume so we know that the planet's volume is greater than Earth's - that means its radius will be greater.
1.5
1

Average density of the planet

See the comment in mass
1
1

Time for the planet to rotate once on its own axis

Time for rotation on its own axis is the day length.
0.85
1

Speed of the planet in its orbit

The further away a planet is from the star it orbits, the smaller the pull of gravity, and the smaller speed it needs to stay in orbit.
0.82
1

Angle of tilt of the planet's axis

The bigger the tilt of the planet's axis the more dramatic the changes in seasons will be.
23o
0o

Acceleration of an object freely falling near to the planet's surface

The gravitational field strength in N/kg is the same value as the acceleration due to gravity in m/s2.
11 m/s2
10 m/s2

 

(a) In her story, how should the writer compare conditions on Delta with those on Earth? Tick the correct box in each case.

greater
less
same
length of year
   
length of day
    
radius of the planet
   

 

3 marks

(b) One of the space travellers lands on planet Delta. With her space suit, she has a mass of 100 kg. What is her weight on planet Delta? Don't forget to give the unit.

The gravitational field strength in N/kg is the same value as the acceleration due to gravity in m/s2.

weight = mg = 100 x 11 = 1100 N

2 marks

(c) The inclination of the axis of rotation to the axis of orbit (the 'tilt' of the planet) is different for Delta and Earth.

In the story, the travellers spend a year on Delta. Describe two differences between Delta and Earth that the travellers would find, apart from their weight.

any two from:

  • There would be no seasonal variation on Delta like we have on Earth.
  • Temperature in a region of Delta would be roughly the same all year, whereas on Earth it is colder in winter.
  • There would be no hibernation or migration of animals on the planet Delta as their habitat would have constant conditions.
  • Days and nights on Delta would always the same length - half of the time it takes to rotate on its axis. On Earth the day length increases from mid-winter to mid-summer
  • The Sun would always be directly above equator on Delta - accept 'Sun always follows the same path across the sky'

In questions like this always clearly state which planet you are talking about. It is a good idea to compare the two. Vague answers get no marks from examiners. Express yourself in good clear English - full sentences!

2 marks

Maximum 7 marks