Question

A stone dropped from the top of a building travels 24.5 m in the last second of its fall. Find the height of the tower, (g = 9.8 m/s²)

Answer 1

Distance travelled in the last second of its fall is S_n = 24.5m

Also, S_n = ut + a(n – 1/2)

But u = 0, a = g

∴ S_n = 0 + g(n – 1/2)

24.5 = 9.8n – 4.9

n = (24.5 + 4.9)/9.8 = 3 seconds.

we know that S = ut + 1/2 at²

∴ Height of the tower;

h = 0 × 3 + 1/2 × 9.8(3)²

(∵ s = h, u = 0, a = g = 9.8m/s)

∴ h = 0 + 4.9(3)²

= 44.1m.