A communications truck with a 44-cm-diameter dish receiver on the roof starts out 10 km from its base station. It drives directly away from the base station at 50 km/h for 1.0 h, keeping the receiver pointed at the base station. The base station antenna broadcasts continuously with 2.5 kW of power, radiated uniformly in all directions. How much electromagnetic energy does the truck’s dish receive during that 1.0 h?
radius of dish(r): 44/2 cm= 0.22m
v = 50km/h = 50000m/h = 13.88m/s
Time = 1hr
Energy received by dish is power received over the course of 1hr time period.
____ eq (1)
Now, Intensity received by dish is ,
Where, P = power
A = Area
So, P = IA
Now we know that the truck is moving away from the station at a constant speed. So truck's distance from station at any time t is
Substituting this in equation 3 we get,
Here A =
Substituting this value in above equation we get:
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