Answer:
a) 28877 AU
b) 1.795 sec
Explanation:
Time it took the radio signal to reach earth = 4 hours = 4 x 3600 = 14400 s
speed of radio signal = speed of vacuum speed of light = 3 x 10^8 m/s
Distance traveled by this signal = speed x time
distance = 3 x 10^8 x 14400 = 4.32 x 10^12 m
One Astronomic unit AU is the distance between the Earth and the sun and it is approximately equal to 1.496 x 10^8 m
The distance traveled by the signal in AU = (4.32 x 10^12)/(1.496 x 10^8) = 28877 AU
b) The minimum separation between Earth and Mars = 0.36 AU
This distance = 0.36 x 1.496 x 10^8 = 538560000 m
Time that will be taken for a radio signal to travel this distance = distance/speed
==> 538560000/(3 x 10^8) = 1.795 sec