Two cities are 150 km apart. Electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 volt and the average resistance per km is 0.5 $\Omega$. The power loss in the wire is 
 

Given, distance between the cities d = 150
km
Potential drop = 8 volt per km
Total drop in potential = 150 x 8 = 1200 V
Resistance per km is = 0.5 Ω
The resistance will be equivalent to multiple
resistors in series.
Total resistance = 0.5 x 150 = 75 Ω
The power loss in a resistance is given by
$P=\frac{v^2}{R}$
where v is the voltage or potential difference and R is the resistance.
$\therefore$ Total power loss is
$P=\frac{(1200{)}^2}{75}=19200=19.2\mathrm{kW}$