A ball is dropped from rest. What will be the velocity of the ball after falling 20 m? (Take g = 10 m/s²)

Correct option is B

The correct answer is (b) 20.0 m/s

Explanation:

• We use the third equation of motion:
v² = u² + 2gs

• Initial velocity u = 0, because the ball is dropped from rest.

• Acceleration due to gravity g = 10 m/s².

• Distance fallen s = 20 m.

• Substituting the values:
v² = 0² + 2 × 10 × 20
v² = 400

• Taking the square root:
v = 20 m/s

Information Booster:

• The equations of uniformly accelerated motion are also used for objects in free fall.

• When an object is dropped, its initial velocity is zero.

• Acceleration is taken as positive in the downward direction because gravity pulls objects toward the Earth.

Additional Knowledge:

40.0 m/s (Option a)
• This would occur if the object had fallen about 80 m or had some initial velocity.

50.0 m/s (Option c)
• This would require a fall distance of about 125 m, so it is incorrect.

10.0 m/s (Option d)
• This is the velocity after about 1 second of fall (distance ≈ 5 m), confusing velocity with the value of g.