Question

A stone is dropped from the top of a building strikes the ground with a velocity of 30m/s calculate the height of the building and time taken to reach the ground.

Answer 1

Given:-

• Initial velocity ,u = 30m/s

• Final velocity ,v = 0m/s

• Acceleration due to gravity ,a= 9.8m/s²

To Find:-

• Height of building ,h

• Time taken to reach the ground.

Solution:-

Firstly we calculate the height of the building. By using 3rd Equation of Motion

• v² = u² +2ah

Substitute the value we get

→ 0² = 30² + 2× 9.8×h

→ 0 = 900 + 19.6 × h

→ 900 = 19.6 × h

→ h = 900/19.6

→ h = 45.91 m ≈ 46 m

Therefore, the height of the building is 46 metres.

Now, calculating the time taken , So using 1st Equation of motion

• v = u + at

Substitute the value we get

→ 0 = 30 + 9.8×t

→ t = 30/9.8

→ t = 3.06 s

Therefore, the time taken by the stone is 3.06 seconds.

Answer 2

Answer:

=> v = u + at

=> 0 = 30 + 9.8×t

=> t = 30/9.8

=> t = 3.06 s

time is 3.06 s

And

=>v² = u² +2ah

=> 0² = 30² + 2× 9.8×h

=> 0 = 900 + 19.6 × h

=> 900 = 19.6 × h

=> h = 900/19.6

=> h = 45.91 m

Height is 45.91 metre.