Question

A stone is let to fall from a building of height 80m. What will be the ratio of heights
fallen by the stone after 2s and 3s?

Answer 1

Answer:

4 : 9

Explanation:

Stone is free falling from a height. So, initial velocity, u = 0

• Velocity in 2s and 3s i.e V1 and V2 can be found out by the first equation of motion

v = u+ at

where v = final velocity

u= initial velocity

a = acceleration due to gravity = 10m/s² ( for easy calculation)

t= time

V1 = u + at = 0+ 2×10 = 20m/s

V2 = u + at = 0 + 3×10 = 30m/s

Distance covered by the stone can be found out by the third equation of motion v²-u²= 2as

Distance covered in 2 secs ,

V1²-u² = 2as

→ 400- 0 = 20s

→ s = 20 m

Distance covered in 3 secs ,

V2²-u² = 2as

→ 900- 0 = 20s

→ s = 45 m

Ratio of heights fallen by stone after 2s and 3s = 20/45= 4/9