$A$ particle moves in the $XY$-plane with $x$ and $y$ coordinates varying with time $t$ as $x(t) = 5t$ and $y(t) = 5t(27 - t^2)$. At what time $t$ (in seconds) will the direction of velocity and acceleration be perpendicular to each other?

In the figure shown,the two projectiles are fired simultaneously. The minimum distance between them during their flight is ........ $m$.

$A$ point $P$ on the circumference of a wheel is initially in contact with the ground. If the radius of the wheel is $5 \, m$,what will be the displacement of point $P$ when the wheel rolls forward by half a revolution?

$A$ stone of mass $m$ is tied to a string of length $l$ and rotated in a circle with a constant speed $v$. If the string is released,the stone flies:

$A$ car moving with a linear speed of $72 \ km/h$ has wheels of radius $0.250 \ m$. If the wheels come to rest after $20$ rotations upon applying brakes,the angular retardation produced by the brakes is ....... $rad \ s^{-2}$. (in $.5$)

Read each statement below carefully and state,with reasons,if it is true or false:
$(a)$ The net acceleration of a particle in circular motion is always along the radius of the circle towards the centre.
$(b)$ The velocity vector of a particle at a point is always along the tangent to the path of the particle at that point.
$(c)$ The acceleration vector of a particle in uniform circular motion averaged over one cycle is a null vector.