$$y=\left(P t^2-Q t^3\right) \mathrm{~m}$$ is the vertical displacement of a ball which is moving in vertical plane. Then the maximum height that the ball can reach is

A car covers a distance at speed of $$60 \mathrm{~km} \mathrm{~h}^{-1}$$. It returns and comes back to the original point moving at a speed of $$v$$. If the average speed for the round trip is $$48 \mathrm{~kmh}^{-1}$$, then the magnitude of $$v$$ is

The displacement of a particle starting from rest at $$t=0$$ is given by $$s=9 t^2-2 t^3$$. The time in seconds at which the particle will attain zero velocity is

Two cars A and B are moving with a velocity of 30 km/h in the same direction. They are separated by 10 km. The speed of another car C moving in the opposite direction, if it meets these two cars at an interval of eight minutes is