The radius of a wheel of a car is $21 \, cm$. If it makes $800$ rotations per minute,find the speed of the car in $km/h$.

It is proposed to build a single circular park equal in area to the sum of areas of two circular parks of diameters $16 \, m$ and $12 \, m$ in a locality. The radius of the new park would be (in $m$)

The area of a circular playground is $22176 \, m^{2}$. Find the cost of fencing this ground at the rate of $Rs. \, 50$ per $metre$. (in $Rs.$)

The area of a circle is $3850 \, cm^2$. In that circle,the length of an arc subtending a right angle at the centre is $\ldots \ldots \ldots \, cm$.

In a circle with radius $14 \,cm$,an arc subtends a right angle at the centre. Find the length of this arc,the area of the minor sector,and the area of the minor segment formed by it.

In a circle with radius $14 \, cm$,$\overline{OA}$ and $\overline{OB}$ are radii perpendicular to each other. Then,the area of the minor sector corresponding to $\angle AOB$ is $\ldots \ldots \ldots \, cm^2$.