A parachutist bails out from an aeroplane and after dropping through a distance of 40m opens the parachute and decelerates at 2 ms–2. If he reaches the ground with a speed of 2 ms–1 how long is he in the air? At what height did he bail out from the plane?

Formula to be used:

..1


..2


..3


Where v = Final Velocity t = Time


u = Initial Velocity s = Distance


a = Acceleration


Two Cases:


(1) Parachutists undergo a freefall for 40 m


(2) Parachutists decelerates at 2 ms–2 and reach ground at a speed of 2 ms–1


Case – 1:


Here, u = 0; s = ; a = g = Acceleration due to gravity; v = ? ; t = = ?


Now, using equation 3, we get:




..4


Now, this speed becomes the initial speed for case 2.


Also, using equation 1, we get:




..5


Case – 2:


Here, u = ; a = –2 ms–2; t = ? ; s = ? ; v = 2 ms–1


Now, using equation 3, we get:




..6


Also, using equation 1:




..7


So, total time taken =


Also, total distance above ground =


= 40 + 195


= 235 m


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