Question

A ball thrown up vertically returns to the thrower after 6 s. The velocity with which it was thrown up is (Take $g=9.8m{s}^{-2}$)

• A. $24.9m{s}^{-1}$
• B. $29.4m{s}^{-1}$
• C. $39.4m{s}^{-1}$
• D. $34.9m{s}^{-1}$

Answer 1

The correct option is B

$29.4m{s}^{-1}$

Time of ascent is equal to the time of descent. The ball takes a total of 6 s for its upward and downward journey.
Hence, it has taken 3 s to attain the maximum height.
Final velocity of the ball at the maximum height, v = 0
Acceleration due to gravity, $g=-9.8m{s}^{-2}$
From the first equation of motion,
v = u + gt
$0=u+(-9.8\times 3)$
$u=9.8\times 3=29.4m{s}^{-1}$
Hence, the ball was thrown upwards with a velocity of $29.4m{s}^{-1}$