Question Details

If ratio between volume of a cylinder and volume of sphere is 3 : 1, then find the ratio between total surface area of cylinder to total surface area of sphere, radius of sphere is equal to radius of cylinder?

Options

A

2 : 1

B

5 : 2

C

4 : 1

D

3 : 2

Show Answer

Correct Answer :

Option B

5 : 2

5 : 2

Solution :

The correct option is 5 : 2.

Let the radius of the sphere be r and the radius of the cylinder also be r, since they are given to be equal. Let the height of the cylinder be h.

First, we express the volume of the cylinder (Vc) and the volume of the sphere (Vs):
Vc=πr2h
Vs=43πr3

We are given that the ratio of the volume of the cylinder to the volume of the sphere is 3 : 1.
VcVs=31

Substitute the formulas for volume into the ratio:
πr2h43πr3=3

Simplify the equation by canceling π and r2:
h43r=3
3h4r=3

Dividing both sides by 3, we get:
h4r=1
h=4r

Now, we find the ratio between the total surface area of the cylinder (TSc) and the total surface area of the sphere (TSs).
The formula for the total surface area of a cylinder is:
TSc=2πr(r+h)

Substitute h=4r into the cylinder's surface area equation:
TSc=2πr(r+4r)=2πr(5r)=10πr2

The total surface area of the sphere is:
TSs=4πr2

Now, find the ratio of their total surface areas:
TScTSs=10πr24πr2

Cancel πr2 from the numerator and the denominator:
TScTSs=104=52

Therefore, the ratio of the total surface area of the cylinder to the total surface area of the sphere is 5 : 2.

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