Question

A body falls from a height of 120 m. After 2 s of fall, if gravity disappears then total time taken to reach the ground is (g = 10 m/s Square)
(a) 9 s (b) 5 s (c) 7 s (d) 10 s

Answer 1

h = 120 meters

v = u + g t 
   = 0 + 10 m/s/s * 2 sec = 20 m/s
distance traveled in 2 sec 
  s = u t + 1/2 g t^2 = 0 + 1/2 *  10 * 2^2 = 20 meters

Distance to travel = 120 - 20 = 100 m
velocity = 20 m/sec   is constant as there is no gravity.

time taken = 100 m/ 20 m/s   = 5 seconds

Answer 2

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u = 0 m/s
t = 2 seconds
g = 10 m/s​2
h = ut + 1/2 g t2
h = 0 + 1/2 (10) 4 = 20 m
Remaining Distance = 199-20 = 179 m
v = u + gt = 0 + 10 x 2 = 20 m/s
Now, we have v = 20 m/s, no gravity and distance = 179 m
So, time = distance/speed = 179/20 = 89.5 seconds
So, total time = 89.5+2 = 91.5 seconds