Question

how long will a stone take to fall from the top of a building 80 metre high and what will be the velocity of the stone or reaching on the ground
$....$
g = 10 m/s2​

Answer 1

Answer:

Time taken,t :- 4 second

Final Velocity, V :- 40m/s

Explanation:

Answer is attached with full process

Answer 2

Stone will take 4 seconds to reach ground and velocity of stone on reaching ground is 40 m/s.

Solution

As the stone is dropped freely from the top of a building,so initial speed of stone i.e. u = 0 m/s

Height of building (h) = 80 m

Gravitational acceleration (g) = 10 m/s²

We will use 2nd equation of motion to find time taken to reach ground.

We know for a free falling body,

● h = ½ gt²

⇒ 80 = ½ × 10 × t²

⇒ 80 = 5t²

⇒ t² = 80/5

⇒ t² = 16

⇒ t = √16

⇒ t = 4 seconds.

∴ Time taken to reach ground = 4 seconds.

Now we will use 3rd equation of motion to find final velocity of stone :

● v² = u² + 2gh

⇒ v² = 0² + 2 × 10 × 80

⇒ v² = 1600

⇒ v = √1600

⇒ v = 40 m/s

∴ Final velocity of stone while reaching ground = 40 m/s