Water drops fall from a tap on the floor, 5 m below, at regular intervals of time, the first drop strikes the floor when the sixth drop begins to fall. The height at which the fourth drop will be from ground, at the instant when the first drop strikes the ground is m. (g = 10 m/s2)
- 3.8
- 4.0
- 4.2
- 2.5
Answer
(3) 4.2
Solution
Let the time interval between two drops be .
When the 1st drop strikes the floor, the 6th drop just begins to fall the 1st drop has fallen for 5 .
h = 12g(5 )2
5 = 12 10 25 2
2 = 0.04 s2, = 0.2 s
The 4th drop has fallen for 2 = 0.4 s:
s4 = 12 10 (0.4)2 = 0.8 m
Height of the 4th drop above the ground = 5 - 0.8 = 4.2 m
Answer: (3)