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 ___

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

Q. 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)

(A) 3.8

(B) 4.0

(D) 2.5

Correct Answer: 4.2 m

Explanation

Let the time interval between successive drops be t.

The first drop strikes the ground when the sixth drop just begins to fall, so the time of fall of the first drop is:

The height of the tap from the ground is 5 m, so using the equation of motion:

5 = ½ g (5t)²

5 = ½ × 10 × 25t²

t² = 0.04

The fourth drop has been falling for:

(5 − 4)t = 2t

Distance fallen by the fourth drop in time 2t:

s = ½ g (2t)² = ½ × 10 × 4t² = 20t²

s = 20 × 0.04 = 0.8 m

Therefore, height of the fourth drop from the ground is:

5 − 0.8 = 4.2 m

Explanation

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