(a) How long in seconds does it take a radio signal to travel 220 km from a transmitter to a receiving antenna? (b) We see a full Moon by reflected sunlight. How much earlier did the light that enters our eye leave the Sun? The Earth – Moon and Earth – Sun distances are 3.8x105 km and 1.5 × 108 km, respectively. (c) What is the round-trip travel time in seconds for light between Earth and a spaceship at a 7.5 × 108 km distance from Earth? (d) Suppose astronomers observe a supernova about 7200 light-years (ly) distant. How long ago in years did the explosion actually occur?

a) , b) , c) , d) 7200 years ago.

Explanation:

The speed of light is equal to .

a) Radio signal is a form of electromagnetic waves, which does not need a medium in which to propagate. The time required is:

b) The time required is:

c) The round-trip travel time is:

d) A light-year is distance unit which is equal to the distance travelled by light during one year. Hence, the observation of the supernova happened about 7200 years ago.

this one:

as we gain mass the force of gravity on us increases.

pls mark me as the ! : d

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