Question

A man throws a ball vertically upward and it rises through 20 m and returns to his hands. What was the initiasl velocity $(u)$ of the ball and for how much time $(T)$ it remained in the air $\lbrack g = 10m/s^{2}\rbrack$

• A. u = 10 m/s, T = 2s
• B. u = 10 m/s, T = 4s
• C. u = 20 m/s, T = 2s
• D. u = 20 m/s, T = 4s

Answer 1

Answer: (D)

u = 20 m/s, T = 4s

Answer 2

$u = \sqrt{2gh} = \sqrt{2 \times 10 \times 20} = 20\mspace{6mu} m/s$

and $T = \frac{2u}{g} = \frac{2 \times 20}{10} = 4$sec