Pedalling a bicycle into a 30 km/h wind requires how much more effort compared to pedalling into a 10 km/h wind?
A)eighteen times as much
B)nine times as much
C)six times as much
D)three times as much

Question

Quizplus · Accepted Answer

The effort required to overcome air resistance increases with the cube of the velocity. Therefore, pedalling into a 30 km/h wind (3 times the speed of a 10 km/h wind) requires 3^3 = 27 times the effort. However, since you're already putting in effort to overcome the 10 km/h wind, the additional effort is 27 - 1 = 26 times the effort for the 10 km/h wind. The correct interpretation of the question suggests comparing the effort at 30 km/h directly to 10 km/h, which is a common misunderstanding. The direct comparison should indeed reflect that the effort increases with the cube of the speed difference. However, the options provided do not accurately reflect the precise calculation based on the cube law, suggesting a misunderstanding in the explanation. The principle that the drag force (and thus the effort) increases with the square of the velocity should guide the correct answer, but the options and explanation seem misaligned with this physical law. Re-evaluating the explanation: The drag force, which determines the effort, indeed increases with the square of the velocity relative to the air. If the velocity triples (from 10 km/h to 30 km/h), the effort increases by a factor of 3^2 = 9, making option B the intended correct choice based on a simplified interpretation focusing on the square law for drag force in the context of the provided options.

Pedalling a Bicycle into a 30 Km/h Wind Requires How