A train is moving along a straight line with a constant acceleration $a$. A boy standing in the train throws a ball forward with a speed of $10{ \mathrm{m} \mathrm{s}}^{-1}$ at an angle of $60°$ to the horizontal. The body has to move forward by $1.15 \mathrm{m}$ inside the train to catch the ball back to the initial height. The acceleration of the train, in $\mathrm{m} {\mathrm{s}}^{-2}$ is,

Airplanes $A$ and $B$ are flying with constant velocity in the same vertical plane at angles $30°$ and $60°$ with respect to the horizontal respectively as shown in the figure. The speed of $A$ is $100\sqrt{3}{ \mathrm{m} \mathrm{s}}^{-1}$. At time $t=0 \mathrm{s}\text{,}$ an observer in $A$ finds $B$ at a distance of $500 \mathrm{m}.$ This observer sees $B$ moving with a constant velocity perpendicular to the line of motion of $A.$ If at $t=t_0, A$ just escapes being hit by $B, t_0$ in seconds is