A rectangular sheet of dimensions 25 cm×7 cm is rotated about its longer side. Find the whole surface area of the solid thus generated.
When a rectangular sheet is rotated about its length, we get a cylinder
where the height of cylinder =7 cmand the circumference of the base of the cylinder =25 cm
Thus curved surface area =2πrh
=(2πr)×h
=25×7
=175 cm2