Question

A ball of mass $0.2kg$ is thrown vertically upwards by applying a force by hand. If the hand moves $0.2m$ while applying the force and the ball goes upto $2m$ height further, find the magnitude of force applied by the hand. Consider $g=10$ ${ms}^{-2}$.

• A. $20N$
• B. $22N$
• C. $4N$
• D. $16N$

Answer 1

Answer: (B)

$22N$

The height attained by the ball $h=2m$

So, the velocity of ball when leaving the hand $=\sqrt{2gh}=\sqrt{40}m/s$

By using 3rd equation of motion for the duration while the force was applied,

$v^2-u^2=2as$
$40=2\times a\times 0.2$
$a=100m/s^2$

By Newton's second law of motion,
$F_{net}$ = Mass of ball $\times$ acceleration $=20$ N in upward direction
$F_{net}=F_{hand}-F_{gravity}$
$F_{hand}$ = $20+mg=20+(0.2\times 10)$
$F_{hand}=22N$