Question

A stone is dropped from a height of 20 m.

(i) How long will it take to reach the ground?
(ii) What will be its speed when it hits the ground? (g = 10 m/s²)

Answer 1

(i) s (distance) = 20m
u (initial velocity) = 0 m/s
a (acceleration due to gravity i.e., g) = 10m/s²
t (time) = ?
S = ut +1/2 gt²
20 = 0×t + ½ ×10 ×t²
20 = ½ ×10×t²
20×2 = 10t²
20×2 ×10 = t²
t² = 4
t = 2
Answer: time = 2 sec

(ii). v (final velocity) = ?
u (initial velocity) = 0 m/s
a (acceleration due to gravity i.e., g) = 10m/s²
t (time) = 2 sec
v = u + gt
= 0 + 10 × 2
= 20m/s
Answer: v = 20 m/s