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PHYSICS, M5 2023 VCE 2

Phobos is a small moon in a circular orbit around Mars at an altitude of 6000 km above the surface of Mars.

The gravitational field strength of Mars at its surface is 3.72 N kg. The radius of Mars is 3390 km.

  1. Show that the gravitational field strength 6000 km above the surface of Mars is 0.48 N kg.   (2 marks)
  1. Calculate the orbital period of Phobos. Give your answer in seconds.  (3 marks)
  1. Phobos is very slowly getting closer to Mars as it orbits.
  2. Will the orbital period of Phobos become shorter, stay the same or become longer as it orbits closer to Mars? Explain your reasoning.  (2 marks)

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a.    \(0.48\ \text{N kg}^{-1}\)

b.   

c.    The orbital period will become shorter.

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a.   

        
 
   
   

 
 

        
   
   

 

b.    
 
   
   
   

♦ Mean mark (b) 53%. 
COMMENT: Rounded calculations, such as using 6.41 × 10^23 were marked as wrong.

c.    

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PHYSICS, M5 2023 VCE 3 MC

Space scientists want to place a satellite into a circular orbit where the gravitational field strength of Earth is half of its value at Earth's surface.

Which one of the following expressions best represents the altitude of this orbit above Earth's surface, where is the radius of Earth?

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Show Worked Solution

→ For gravitational field strength,

→ Therefore if → , the radius will become .

→ Thus the altitude above the surface of the earth is .

♦♦ Mean mark 39%.

PHYSICS, M5 EQ-Bank 21

Planet has a mass eight times that of Earth. The acceleration due to gravity on the surface of this planet is half that on the surface of Earth.

If Earth has a radius of 1, what is the radius of Planet ?   (3 marks)

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Radius of Earth:

 
 
   
 

 
Radius of planet :

 
   
 
   

 
Since Earth has a radius of 1