A tap is 5 m above the ground. Water drops fall at equal intervals. When the 6th drop leaves the tap, the first drop reaches the ground. Find the distance travelled by the 4th drop at that instant.

Solution:

Let time interval between successive drops be T.

When the 6th drop falls:

Time taken by first drop = 5T

Using:

s = ½gt²

5 = ½ × 10 × (5T)²

5 = 125T²

T² = 1/25

T = 0.2 s

The 4th drop has been falling for:

2T = 0.4 s

Distance travelled:

s = ½ × 10 × (0.4)²

= 0.8 m

Answer: 0.8 m