The surface area of a sphere is $2464 \, cm^2$. Find its diameter in $cm$.

In $\triangle ABC$,$\angle B = 90^{\circ}$,$AB = 28 \, cm$,and $BC = 21 \, cm$. If the triangle is revolved about the side $AB$,find the curved surface area of the cone so obtained. Similarly,if the triangle $ABC$ is revolved about the side $BC$,find the curved surface area of the cone so obtained.

Write True or False and justify your answer in each of the following:
If the radius of a cylinder is doubled and its curved surface area is not changed,the height must be halved.

For a given cylinder,the diameter of the base is $7 \,cm$ and its height is $12 \,cm$. Find the curved surface area of a cylinder (in $cm^2$).

Find the total surface area of a cylinder with diameter $28 \text{ cm}$ and height $50 \text{ cm}$. (in $\text{cm}^2$)

Find the curved surface area and the total surface area of a hemisphere with a diameter of $14 \, cm$.