Answer:
[tex] 50[/tex] Watt
Explanation:
[tex]P_{1}[/tex] = Initial signal power = 2 Watts
[tex]r_{1}[/tex] = Initial range of distance to which signal is received = 3 miles
[tex]P_{2}[/tex] = Final signal power = ?
[tex]r_{2}[/tex] = Final range of distance to which signal is received = 15 miles
Intensity is inversely proportional to square of the distance from the source, hence
[tex]\frac{P_{1}}{{r_{1}}^{2}} = \frac{P_{2}}{{r_{2}}^{2}}[/tex]
[tex]\frac{2}{{3}^{2}} = \frac{P_{2}}{{15}^{2}}[/tex]
[tex]\frac{2}{9} = \frac{P_{2}}{225}[/tex]
[tex]P_{2} = \frac{2\times 225}{9}[/tex]
[tex]P_{2} = 50[/tex] Watt