13.2. Gravitational force between point masses
A subsection of Physics, 9702, through 13. Gravitational fields
Listing 10 of 55 questions
12 State two reasons why frequencies in the gigahertz (GHz) range are used in satellite communication. 1. 2. In one particular satellite communication system, the frequency of the signal transmitted from Earth to the satellite (the up-link) is 6 GHz. The frequency of the signal transmitted back to Earth from the satellite (the down-link) is 4 GHz. Explain why the two signals are transmitted at different frequencies. A signal transmitted from Earth has a power of 3.1 kW. This signal, received by a satellite, has been attenuated by 185 dB. Calculate the power of the signal received by the satellite. power = W
9702_w13_qp_43
THEORY
2013
Paper 4, Variant 3
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Polar orbiting satellites have orbits over the poles of the Earth. Geostationary satellites are in equatorial orbits. Both are used as part of communication channels. State one advantage and one disadvantage of the use of a polar orbiting satellite as compared with a geostationary satellite. advantage: disadvantage: A geostationary satellite is known to operate on the 6/4 GHz band. Explain what is meant by the 6/4 GHz band, why two different frequencies are necessary.
9702_w15_qp_43
THEORY
2015
Paper 4, Variant 3
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Define gravitational potential at a point. The Earth may be considered to be a uniform sphere of radius 6.4 × 106 m with its mass of 6.0 × 1024 kg concentrated at its centre. A satellite of mass 2.4 × 103 kg is launched from the Equator. It is placed in an equatorial orbit at a height of 5.6 × 106 m above the Earth’s surface. Calculate the change ΔEP in gravitational potential energy of the satellite for its movement from the surface of the Earth to its position in the equatorial orbit. ΔEP = J Determine the speed of the satellite when in orbit. speed = m s–1 Before the satellite in is launched, its speed at the Equator due to the Earth’s rotation is 470 m s–1. Suggest why the energy required to launch the satellite depends on whether the satellite, in its orbit, is travelling from west to east or from east to west.
9702_w20_qp_42
THEORY
2020
Paper 4, Variant 2
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Questions Discovered
55