Question

inner radius and outer radius of hollow cylinder are 8 cm and 10 cm respectively. if its outer surface area is 440 square cms. find its volume and inner surface area ​

Answer 1

Answer:

Step-by-step explanation:

As per given picture External radius =R=8 cm

Internal radius =r (let)

Height =10 cm

Total surface area = 338πcm  

2

 

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(R  

2

−r  

2

)

⇒2π(Rh+rh+R  

2

−r  

2

)=338π

⇒(Rh+rh+R  

2

−r  

2

)=169

⇒(10×8)+(10×r)+(8)  

2

−r  

2

=169

⇒80+10r+64−r  

2

=169

⇒−r  

2

+10r−25=0

⇒r  

2

−10r+25=0

⇒(r−5)  

2

=0

⇒r=5

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