Question

A sky diver jumps from an airplane. After "free falling" for a while, she opens her parachute and her descent speed begins to decrease. While her descent speed decreases, let $F$ denote the magnitude of the gravitational force on the sky diver and let $D$ denote the magnitude of the upward force of air resistance (drag). Which of the following is then true?

• A. $F>D$
• B. $F<D$
• C. $F+D<$ weight of the sky diver
• D. $F-D>$ weight of the sky diver
• E. $F-D>0$

Answer 1

Answer: (B)

$F<D$

Net force acting downward=$F-D=\frac{dv}{dt}$

Since the speed downwards is decreasing after opening the parachute, $dv$ is negative.

Thus $F-D=\frac{dv}{dt}<0$

$⟹F<D$