When a ball is dropped from a height without air resistance, it undergoes free fall motion due to the force of gravity. We can calculate its velocity just before hitting the ground using the equations of motion.
The relevant equation for this scenario is:
v^2 = u^2 + 2as
Where: v = final velocity u = initial velocity (0 m/s, as the ball is initially at rest) a = acceleration due to gravity (-9.8 m/s^2, assuming downward as positive) s = displacement (height, -20 m as it is downward)
Substituting the given values:
v^2 = 0^2 + 2 * (-9.8) * (-20) v^2 = 0 + 392 v^2 = 392 v = √392
Taking the square root of 392:
v ≈ 19.8 m/s
Therefore, the velocity of the ball just before hitting the ground, assuming no air resistance, is approximately 19.8 m/s.