The motion of a stone thrown vertically upward is given by $s = 13.8t - 4.9t^2$,where $s$ is in meters and $t$ is in seconds. Then its velocity at $t = 1$ second is ........ $m/s$.

The rate of change of the area of a circle with respect to its radius $r$ at $r = 6 \text{ cm}$ is

If the rate of increase of the surface area of a spherical balloon is $5 \text{ cm}^2/\text{sec}$ and the rate of increase of its volume is $10 \text{ cm}^3/\text{sec}$, then the radius of the balloon at that instant is... (in $\text{ cm}$)

If water is poured into a cylindrical tank of radius $3.5 \ ft$ at the rate of $1 \ ft^3/min$, then the rate at which the level of the water in the tank increases (in $ft/min$) is

$A$ particle moves in a straight line in such a way that its velocity at any point is given by $v^2 = 2 - 3x$,where $x$ is measured from a fixed point. The acceleration is

If the surface area of a sphere of radius $r$ is increasing uniformly at the rate $8 \, cm^2/s$,then the rate of change of its volume is