QuestionJune 21, 2025

At one instant a heavy object in air is moving upward at 20m/s Five seconds later its speed is approximately 50m/s 30m/s 70m/s 40m/s

At one instant a heavy object in air is moving upward at 20m/s Five seconds later its speed is approximately 50m/s 30m/s 70m/s 40m/s
At one instant a heavy object in air is moving upward at 20m/s Five seconds later its speed is approximately 50m/s 30m/s 70m/s 40m/s

Solution
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Answer

-29 \, \text{m/s} (The object is moving downward at this speed.) Explanation 1. Identify the acceleration The object is moving under gravity, so the acceleration a = -9.8 \, \text{m/s}^2 (negative because it's upward). 2. Use the velocity formula Use **v = u + at** where u = 20 \, \text{m/s}, t = 5 \, \text{s}, and a = -9.8 \, \text{m/s}^2. 3. Calculate final velocity v = 20 + (-9.8) \times 5 = 20 - 49 = -29 \, \text{m/s}.

Explanation

1. Identify the acceleration<br /> The object is moving under gravity, so the acceleration $a = -9.8 \, \text{m/s}^2$ (negative because it's upward).<br />2. Use the velocity formula<br /> Use **$v = u + at$** where $u = 20 \, \text{m/s}$, $t = 5 \, \text{s}$, and $a = -9.8 \, \text{m/s}^2$.<br />3. Calculate final velocity<br /> $v = 20 + (-9.8) \times 5 = 20 - 49 = -29 \, \text{m/s}$.
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