If it takes an object 3s to fall freely to the ground from a certain height, what is the distance covered by the object?

Analyze the question: An object falls freely (starting from rest) for 3 s. We need the distance it covers.

Concept: For free fall from rest, the equation of motion is:

s = ut + ½gt²

where u = 0 (starts from rest), g = acceleration due to gravity, t = time.

JAMB usually takes g = 10 m/s².

Solution:

• u = 0
• t = 3 s
• g = 10 m/s²

s = (0)(3) + ½ × 10 × (3)² s = ½ × 10 × 9 s = 5 × 9 s = 45 m

Answer: The distance covered is 45 m, which is option C.

(If you used g = 9.8 m/s², you would get about 44.1 m, which is still closest to 45 m.)

Tip: When a free-fall question gives no value of g, use 10 m/s². A quick shortcut is s = 5t², so for t = 3 s you get 5 × 9 = 45 m. Also remember the distances for the first few seconds: 5 m, 20 m, 45 m, 80 m (for 1 s, 2 s, 3 s, 4 s). They are 5 times the perfect squares.