# Mensuration-4

### From Homeworkwiki

**A cylindrical pipe has inner radius of 7 cm and water flows through it at 385 liters per minute.**

**Find the rate of flow of water per hour. 1 liter = 1 cu. dm.**

**Solution:** 1 liter = 1 cu. dm

Therefore, 385 liters = 385 cu. dm

= 385 x 1/10 x 1/10 x 1/10 cu. m

= 77/200 cu. m

Flow of water per minute = 77/200 cu. m

Flow of water per hour = 77/200 x 60 = 23.1 cu.m

Now inner radius of the pipe = 7 cm = 7/100 m

Let l be the length of water that flows per hour

Therefore, volume of water that flows per hour = π r^{2} l

Implies, 22/7 x 7/100 x 7/100 x l = 23.1

l = 23.1 x 7/22 x 100/7 x 100/7 = 1500m

Rate of flow = 1.5 km / hr