Question

A football is kicked from the roof of a building with a horizontal velocity of 17 m/s. If the building
height is 20 m, how much time does the football take to hit the ground?​

Answer 1

2seconds

Explanation:

for downward motion

u= initial velocity =0

g= 10m/s^2

h=20m

time = t=?

using 2nd equation of motion

h=ut+1/2gt^2

20 = 0 + 5t^2

20/5 = t^2

4=t^2

t =2s

Answer 2

Given :-

Initial velocity = 0 m/s

Height of the building = 20 m

Speed = 17 m/s

To Find :-

Time required by the football to hit the ground.

Solution :-

We know that,

• t = Time
• s = Displacement
• a = Acceleration
• u = Initial velocity

Using the formula,

$\underline{\boxed{\sf Second \ equation \ of \ motion=s=ut+\dfrac{1}{2} at^2}}$

Given that,

Initial velocity (u) = 0 m/s

Acceleration (a) = 10 m/s

Displacement (s) = 20 m

Substituting their values,

⇒ 20 = 0 × t + 1/2 × 10 × t²

⇒ 20 = 0 + 10/2 t²

⇒ 20 = 5t²

⇒ t² = 20/5

⇒ t² = 4

⇒ t = √4

⇒ t = 2 sec

Therefore, time required by the football to hit the ground is 2 sec.