Question

a hollow cylinder ht=24cm outer dia =8cm thickness is 1cm find outer CSA and inner CSA

Answer 1

Answer:

As per given picture External radius =R=8 cm

Internal radius =r (let)

Height =10 cm

Total surface area = 338πcm²

But Total surface area = Area of external cylinder (curved surface area)

+ Area of internal cylinder (curved surface area) + Twice Area of base (ring 2πR+2πr+2π(R²−r²)

⇒2π(Rh+rh+R²−r²)=338π

⇒(Rh+rh+R²–r²)=169

⇒(10×8)+(10×r)+(8)²-r²=169

⇒80+10r+64−r²=169

⇒−r²+10r−25=0

⇒r²–10r+25=0

⇒(r−5)²=0

⇒r=5

So, thickness of metal =R−r=(8−5) cm =3 cm