Surface Area of a Cylinder

[naeagle]

Here's the problem...

The surface area of a cylinder is approx. 395.64 cm squared. If the radius is 7cm, what is the height?

 

[Deleted member 4993]

Here's the problem...

The surface area of a cylinder is approx. 395.64 cm squared. If the radius is 7cm, what is the height?

What is the expression for surface area of a cylinder - in terms of its radius and height?

 

[naeagle]

The expression is 2(pi)r squared+2(pi)rh
I've tried to subtract 7 from 395.64 and also tried to subtract 7 from 395.64 but not gotten the volume when I do the expession with the number in it.

2(pi)7 squared+2(pi)7*388.64
17401.15604

2(pi)7 squared+2(pi)7*346.64
15553.89956

 

[Deleted member 4993]

The expression is 2(pi)r squared+2(pi)rh
I've tried to subtract 7 from 395.64 and also tried to subtract 7 from 395.64 but not gotten the volume when I do the expession with the number in it.

2(pi)7 squared+2(pi)7*388.64
17401.15604

2(pi)7 squared+2(pi)7*346.64
15553.89956

Your expression is correct - however your manipulations are all wrong:

\(\displaystyle S\, =\, 2\cdot \pi \cdot r^2 \, + \, 2\cdot \pi \cdot r \cdot h\)

\(\displaystyle 2\cdot \pi \cdot r \cdot h \, = \, S \, - \, 2\cdot \pi \cdot r^2\)

\(\displaystyle h \, = \, \frac{S \, - \, 2\cdot \pi \cdot r^2}{2\cdot \pi\cdot r}\)

Now evaluate h

 

[naeagle]

I think I have it!!! Is it 2?

 

[Deleted member 4993]

Check it yourself!

Use this value in the expression for the surface area - and see what do you get!

If you get the surface area to be equal to (or almost equal to) the given value - then most probably you are correct.

If not - then you have made a mistake - somewhere.