Question

Two boys playing tennis on the top floor of the terrace which is at the height of 80 m
from the ground and one boy hit the ball and it is flown off the building with speed 18
m/s. Calculate the speed of the ball just before it reaches the ground. (Ignore air
resistance)​

Answer 1

Answer

• Speed of the ball just before it reaches the ground is 43.86 m/s

Given

• Two boys playing tennis on the top floor of the terrace which is at the height of 80 m  from the ground and one boy hit the ball and it is flown off the building with speed 18  m/s

To Find

• Speed of the ball just before it reaches the ground

⇒ Final velocity , v

Concept Used

We need to apply 3 rd equation of motion

• v² - u² = 2as

Solution

Height , s = 80 m

Initial velocity , u = 18 m/s

Acceleration due to gravity , a = g = 10 m/s²

Final velocity , v = ? m/s

Apply 3 rd equation of motion .

⇒ v² - u² = 2as

⇒ v² - 18² = 2(10)(80)

⇒ v² - 324 = 1600

⇒ v² = 1924

⇒ v = 43.86 m/s