Problem

(II) (a) What is the acceleration of two falling sky divers (total mass = 132 kg including parachute) when the upward force of air resistance is equal to one-fourth of their weight? (b) After opening the parachute, the divers descend leisurely to the ground at constant speed. What now is the force of air resistance on the sky divers and their parachute? See Fig. 4-44.

Solution 17P: The force (friction) due to air is responsible of lowering the net force due to gravity and with the help of parachute the skydivers can be brought safely on the ground. Step 1 of 3 Concept: Newton’s second law: The force F acts on mass m produces an acceleration a in the object. Mathematically, F=ma. Step 2 of 3 A] When parachute was not opened Figure below shows the free body diagram of the two falling sky divers falling vertically downward under gravity. T Upward air resistance mg Combined weight of two divers and parachute due to gravity Since upward force due to air resistance is equal to one-fourth of their combined weight, mg therefore, T = 4 132×9.8 T = 4 T = 323.4 N Therefore, force due to the upward air resistance is T = 323.4 N.