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Gravitational fields - Multiple Choice

Q11. When at the surface of the Earth, a satellite has weight W and gravitational potential energy U.

It is projected into a circular orbit whose radius is equal to twice the radius of the Earth.

Which line, A to D, in the table shows correctly what happens to the weight of the satellite and to its gravitational potential energy?

 

weight

gravitational potential energy

A

becomes W/2

increases by U/2

B

becomes W/4

increases by U/2

C

remains W

increases by U

D

becomes W/4

increases by U

 

Q12. The sketch graph shows how the gravitational potential, V, varies with the distance, r , from the centre of the Earth.


What does the gradient of the graph at any point represent?

A
 the magnitude of the gravitational field strength at that point
B
 the magnitude of the gravitational constant
C
the mass of the Earth
D
the potential energy at the point where the gradient is measured

 

Q13. Near the surface of a planet the gravitational field strength is uniform and for two points, 10 m apart vertically, the gravitational potential difference is 3 J kg–1.

How much work must be done in raising a mass of 4 kg vertically through 5 m?

A
3 J
B
6 J
C
12 J
D
15 J

 

Q14. What would the period of rotation of the Earth need to be if objects at the equator were to appear weightless?

A
 4.5 × 10–2 hours
B
 1.4 hours
C
 24 hours
D
 160 hours

 

Q15. The Earth has density ρ and radius R.

The gravitational field strength at the surface is g.

What is the gravitational field strength at the surface of a planet of density 2ρ and radius 2R?

A
g
B
2 g
C
4 g
D
16 g

 

Q16. Which one of the following graphs correctly shows the relationship between the gravitational force, F, between two masses and their separation r?

 

Q17. Which one of the following could be a unit of gravitational potential?

A
N
B
J
C
N kg–1
D
J kg–1

 

Q18. The radius of a certain planet is x times the radius of the Earth and its surface gravitational field strength is y times that of the Earth.

Which one of the following gives the ratio ?

A
xy
B
x2y
C
xy2
D
x2y2

 

Q19. A planet of mass M and radius R rotates so rapidly that loose material at the equator only just remains on the surface.

What is the period of rotation of the planet?

A
B
C
D

 

Q20. As a comet orbits the Sun the distance between the comet and the Sun continually changes.

As the comet moves towards the Sun this distance reaches a minimum value.

Which one of the following statements is incorrect as the comet approaches this minimum distance?

A
 The potential energy of the comet increases.
B
 The gravitational force acting on the comet increases.
C
 The direction of the gravitational force acting on the comet changes.
D
The kinetic energy of the comet increases.