In free fall, if the upward direction is chosen as the positive $y$-axis, the velocity after time $t$ is
A$v=v_0+gt$
B$v=v_0-gt$
C$v=gt-v_0$ only for downward throws
D$v^2=v_0^2+2gy$
Answer & Solution
Correct answer: B. $v=v_0-gt$
With upward taken as positive, gravitational acceleration is downward, so $a=-g$. Substituting into $v=v_0+at$ gives $v=v_0-gt$.
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