A sky diver jumps from an airplane and initially falls 150 f

A sky diver jumps from an airplane and, initially, falls 150 ft vertically without friction(free fall). At that point his parachute is opened, and he decelerates downward 7 s ft 2 . At the point just before he reaches the ground, his speed is 10 s ft . (a) How long is the parachutist in the air? (b) At what height above the ground did he originally jump?

Solution

                               A

                                                                                                       At point B the velocity is 97.98 ft/s

                                                                                                   V = 2as = 2*32*150 = 97.98ft/s

                                                                                            The time taken to reach ground ‘c’ is t= (v-u)/a

                                                                                            (10-97.98)/7 = 12.57 s    as a = 7ft/s^2

                                             150 ft                                    distance from B to C is (v^2 –u^2)/2*a = 678.6ft

                                                                                         Total distance is 150+ 678.58 = 828.57 ft

                 97.98 ft/s

            B                                           

C                                                            Ground