Circular discs of 5mm thickness, are placed one above the other to form a cylinder of curved surface area 462cm2. Find the number of discs, if the radius is 3.5cm.
Thickness of each disc =5mm=510cm=0.5cm
Radius of disc =3.5cm.
Curved surface area of cylinder =462cm2
∴2πrh=462 ....... (i)
Let the no of discs be x
∴ Height of cylinder, h= Thickness of disc × no of discs=0.5x.......(ii)
From (i) and (ii) we get
2×227×3.5×0.5x=462
∴x=462×72×22×3.5×0.5=42 discs