If the distance $s$ metres traversed by a particle in $t$ seconds is given by $s = t^3 - 3t^2$,then the velocity of the particle when the acceleration is zero,in $m/s$ is:

$A$ stone is dropped into a quiet lake and waves move in circles at the speed of $5 \text{ cm/s}$. At the instant when the radius of the circular wave is $8 \text{ cm}$,how fast is the enclosed area increasing?

The radius of a circular plate is increasing at the rate of $0.01 \text{ cm/s}$ when the radius is $12 \text{ cm}$. Then,the rate at which the area increases,is

$A$ balloon,which always remains spherical,has a variable radius. Find the rate at which its volume is increasing with respect to its radius when the radius is $10 \text{ cm}$.

$A$ stone,thrown vertically upward from the surface of the moon at a velocity of $24 \ m/s$,reaches a height of $s = 24t - 0.8t^2$ meters after $t$ seconds. The acceleration due to gravity in $m/s^2$ at the surface of the moon is:

$A$ water tank has the shape of a right circular cone with its axis vertical and vertex downwards. Its semi-vertical angle is $\tan^{-1} \frac{3}{4}$. Water is poured into it at a constant rate of $6 \text{ m}^3/\text{hr}$. The rate (in $\text{m}^2/\text{hr}$) at which the wet curved surface area of the tank is increasing when the depth of water in the tank is $4 \text{ m}$ is: