Final answer:
The speed of the bullet when it hits the ground on its return is given by the expression v = √(2gh + v₀²), where g is the acceleration due to gravity, h is the height from which the bullet was fired, and v₀ is the initial velocity of the bullet.
Step-by-step explanation:
When the bullet hits the ground on its return, its speed is given by the expression:
v = √(2gh + v₀²)
where g is the acceleration due to gravity, h is the height from which the bullet was fired, and v₀ is the initial velocity of the bullet. This equation is a more general form of the kinematics equation v = √(v₀² + 2ad), which is valid only for constant acceleration.