A ball is dropped off a high building and strikes the ground with an impact velocity of 30 m/s. The height of the building must be ________.

Choose the correct option.

Given: 
The initial velocity of the ball (u)=0.
The final velocity of the ball when it reaches the ground is (v)=30m/s
Acceleration, a= Gravitational acceleration (g)=10 m/s²
Height (h) =?
Substituting the values in the kinematical equation,   
v²−u²=2ah
∴ 30²−0²=2×10×h            
⇒h=45 m

Therefore, the height of the building must be 45 m.