Two particles $A$ and$B$ are thrown vertically upward with velocity, $5 \mathrm{m}$ ${\mathrm{s}}^{-1}$ and $10 \mathrm{m}{ \mathrm{s}}^{-1}$, respectively $(g=10$$\mathrm{m} {\mathrm{s}}^{-2}$ ). Find separation between them after $1 \mathrm{s}$.

A ball is thrown downwards with a speed of $20{ \mathrm{m} \mathrm{s}}^{-1}$ from the top of a building $150 \mathrm{m}$ high and simultaneously another ball is thrown vertically upwards with a speed of $30{ \mathrm{m} \mathrm{s}}^{-1}$ from the foot of the building. Find the time after which both the balls will meet. $\left(g=10{ \mathrm{m} \mathrm{s}}^{-2}\right)$