Question

A spaceman jumps from an airplane. After he had fallen 35 m, then his parachute opens. Now he falls with retardation of 1.8 m/s² and reaches the earth with a velocity of 2.7 m/s. What was the height of the airplane?

Answer 1

The speed of a spaceman after he had fallen 35 m

$$v_i=\sqrt{2gh}=\sqrt{2\times 9.8\times 35}=26.2\:\rm m/s$$

The distance traveled by spaceman when he falls with retardation

$$d=\frac{v_f^2-v_i^2}{2a}=\frac{2.7^2-26.2^2}{2\times (-1.8)}=189\:\rm m$$

Finally, the height of the airplane

$$H=h+d=35+189=224\:\rm m.$$