Question

A stone is thrown vertically upwards with a velocity of 9.8 ms⁻¹. When will it reach the ground?

Answer 1

The ball will reach the ground after 2 seconds .

For the upward motion -

The ball is thrown with an initial velocity (v1) = 9.8 m/s

When the ball will reach the maximum height the final velocity will be zero (v2=0).

For the upward motion the acceleration due to gravity = -9.8 m/s².

The acceleration will be negative because it acts opposite to the velocity of the ball and slows it down .

Using v2 = v1 + at to find the time

=> 0= 9.8 + 9.8t

=> t= 1 second

height = v1 t + 1/2 at²

=> 9.8 × 1 - 1/2 × 9.8

=> 4.9 m

For the downward motion -

height = 1/2 at'²

=> 4.9 = 1/2 × 9.8 t'²

=> t'² = 1

=> t' = 1 second

Therefore , the total time taken = 1+1

= 2 seconds