The air resistance to a car at 20 kmph is R. The air resistance at 40 kmph will be

Answer: Option C

R = K × A × V² when vehicle speed is about 20 km/hr
Where K = Co-efficient of air resistance
A = Projected area of vehicle
V = Vehicle speed in km/hr
When vehicle speed is about 40 km/hr, speed is doubled so we can write V = 2V
Therefore, R = K × A × (2V)²
R = K × A × 4V²
R = 4K × A × V²
R = 4R