Gravity in the solar systemIB MYP Physics: Subtopic test

1. 1
   Astronomers in Chile compare the planets orbiting the Sun. Mercury is the closest planet to the Sun and Neptune is the furthest.

   (a)

   How does the gravitational force between the Sun and a planet change as the planet's distance from the Sun increases?

   [1 mark]

   • AIt stays the same
   • BIt decreases
   • CIt increases
   • DIt increases and then decreases

   (b)

   Compared with Neptune, how does Mercury move around the Sun?

   [1 mark]

   • AA longer orbital period and a lower speed
   • BA shorter orbital period and a lower speed
   • CThe same orbital period and a higher speed
   • DA shorter orbital period and a higher speed

   (c)

   Explain why Neptune takes much longer than Mercury to orbit the Sun.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A communications satellite orbits the Earth in a circular path at a constant height. Its engines are switched off.

   (a)

   What force keeps the satellite in its orbit?

   [1 mark]

   • AThe gravitational force from the Earth
   • BThe thrust from its engines
   • CFriction with the air
   • DThe gravitational force from the Moon only

   (b)

   The satellite is moved to a lower orbit, closer to the Earth. What happens to its orbital speed?

   [1 mark]

   • AIt decreases
   • BIt stays the same
   • CIt increases
   • DIt becomes zero

   (c)

   Explain why the satellite does not move off in a straight line.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student collects data about four planets. Mercury is 58 million km from the Sun and has an orbital period of 88 days. Earth is 150 million km away with a period of 365 days. Mars is 228 million km away with a period of 687 days. Jupiter is 778 million km away with a period of 4333 days.

   (a)

   Describe the trend in the data and calculate how many times longer Jupiter's orbital period is than Earth's.

   [3 marks]

   (b)

   A student hypothesises that planets further from the Sun orbit at a lower average speed. The length of Mercury's orbit is about 364 million km and the length of Jupiter's orbit is about 4890 million km. Calculate the average orbital speed of each planet in million km per day and evaluate the hypothesis.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The International Space Station (ISS) orbits Earth at a height of about 400 km, where gravity is about 90% as strong as at the surface. Astronauts on board float freely. Private companies are also launching thousands of small satellites into orbit around Earth, to provide internet access to remote regions.

   (a)

   Explain why astronauts on the ISS appear weightless even though gravity still acts on them.

   [6 marks]

   (b)

   Discuss and evaluate the launching of thousands of small satellites to provide internet access.

   [6 marks]

   Total for question 4: 12 marks

End of questions