AS Daily A Level Physics question
A skydiver of fixed mass changes posture from spread-eagle to head-first, halving their frontal area. In this speed range, the resistive force of the air is proportional to the square of speed and to frontal area. How does the terminal speed change?
Answer
The correct answer is A.
Correct: A — It increases by a factor of square root of 2 (about 1.41 times). A follows because at terminal speed weight equals drag; with drag proportional to v^2 and area, keeping weight the same gives v proportional to 1/square root of area, so halving area multiplies v by square root of 2. B is wrong because doubling speed would require area to be quartered, not halved. C is wrong because changing frontal area changes the drag at a given speed, so the terminal speed cannot stay the same. D is wrong because reducing area reduces drag at a given speed, so the terminal speed must increase, not decrease.