Question

1) A stone falls from a cliff and travels 34.3m in the last second before it reaches the ground.

Calculate the height of the cliff.

Answer 1

Let the height of the cliff be ‘h’ and suppose it takes ‘n’ seconds to reach the ground.

So, in the nth second it travels 34.3 m.

Using,

Sn = u + (a/2)(2n – 1)

=> 34.3 = 0 + (9.8/2)(2n – 1)

=> n = 4 s

Now, using,

S = ut + ½ at2

=> h = 0 + ½ × 9.8 × 42

=> h = 78.4 m