A ball is thrown vertically upward from the ground with an initial speed of 15 m/s. What is the total time the ball is in the air before it returns to the ground? (Ignore air resistance and take g = 10 m/s².)
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Correct answer
B. 3.0 s
Principle or equation
For vertical motion under constant acceleration due to gravity, the time to reach maximum height is v0/g, and the total flight time is twice that because the upward and downward journeys are symmetric.
Why this answer is correct
The ball's initial upward velocity is 15 m/s. At the highest point, its velocity becomes zero. Using v = v0 - g t, set v = 0: 0 = 15 - 10 t, so t = 1.5 s to reach the top. The return trip takes the same time, so total time = 2 × 1.5 = 3.0 s.
Example
If a ball is thrown upward at 20 m/s, it takes 2 s to reach the top (g=10 m/s²) and 4 s total.
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