Question

A ball thrown up vertically returns to the thrower after 6 s Find it's initial velocity.

• A. 20 m/s
• B. 40 m/s
• C. 35 m/s
• D. 30 m/s

Answer 1

Answer: (D)

30 m/s

The ball returns to the thrower in $6$ s,thus the time for its upward journey$=$$6/2$$=$ 3s
For the upward motion of ball.
Initial velocity $u=$?;final velocity $v=$0
($\because$ Ball comes to rest)
Time ,$t=3$s
Acceleration due to gravity ,$g=-10m{s}^{-2}$
[In upward direction ,$g$ is taken -ve]
$v$$=$$u+gt$
or $0=u-10\times 3,or-u=-30$
or $u=30m{s}^{-1}$
$\therefore$ Initial velocity of ball is $30m{s}^{-1}$