Question

A stone is thrown vertically upwards with a speed of 20 m/s. How high will it go before it begins to fall ? (g =9.8 m/s²)

Answer 1

s (distance) = ?
v (final velocity) = 0 m/s
u (initial velocity) = −20 m/s
a (acceleration due to gravity i.e., g) = 9.8m/s²
υ² − u² = 2as
(0)² − (−20)² = 2 × 9.8 × S
−400 × 2 × 9.8 = S
S = −20.4 m
The negative sign comes because the displacement is upward and we have considered the motion along the acceleration due to gravity (downward) as positive. Thus, the required distance is 20.4 m.
Answer: s = 20.4 m