Question

A stone is dropped from a height of 20 m.

a) How long will it take to reach the ground ?

b) What will be its speed when it hits the ground

take g as 9.8​

Answer 1

$\large\color{orange}\boxed{a.2 seconds</p><p>b.19.7 m/s^-²}$

Answer 2

Solution :

As per the given data ,

• Initial velocity(u) = 0 m/s [ dropped]
• Height (h) = 20 m
• Acceleration due to gravity (g) = 10 m/s²

$\bf{(a)}$As acceleration is uniform throughout it's motion let us use second equation of motion in order to find time (t)

⇒ s = ut + at²/2

⇒ s = 0 x t + 10 x t ²/2

⇒ s = 5t²

⇒ t² = 20/5

⇒ t² = 4

⇒ t = 2 s

The time taken by the stone to reach the ground is 2s .

$\bf{(b) }$Let's use first equation of motion in order to find the final velocity(v)  of the stone .

⇒ v = u + gt

⇒ v = 0 x 9.8  x 2

⇒ v = 19.6  m/s

The speed of the ball when it hit's the ground is 19.6 m/s .