A ball is projected vertically upward with an initial velocity of $50 \mathrm{~ms}^{-1}$ at $t=0 \mathrm{~s}$. At $t=2 \mathrm{~s}$. another ball is projected vertically upward with same velocity.
Att $=$ $\_\_\_\_$ s , second ball will meet the first ball ( $\mathrm{g}=10 \mathrm{~ms}^{-2}$ ).