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The three tennis balls will be staked up like this: O O O So how do you find the HEIGHT of the can? (if you are given only the DIAMETER of one ball?)
I don't really understand what to do...
no that's not right..
The diagram is a good start. Each ball has diameter = 7 cm. So three of them stacked end to end is 3 * 7 = 21 cm. That's the height of the can. The diameter of the can is just the diameter of one ball = 7 cm. Now if you know the HEIGHT of the can (21cm) and the RADIUS of the can (7cm), how can you find the SURFACE AREA of the can? (note: the formula you wrote above was for the VOLUME of the can and that's not what we're looking for).
oh ok the SA is...Ph
but, how did you know to multiply 7 * 3 for the height? did you use a certain formula?
There is no formula. It comes right from the picture. :) O | 7cm O | 7cm O | 7cm add that up and it's 21 cm. :)
oh ok :
Do you mean the diameter of the can is 7? you said radius up above..
Now all you need is the formula for the surface area of a cylinder and you're set. :)
ok, so I dont' have to find the SA of the spheres then?
Sorry. CAN Height = 7*2 = 21 cm Diameter = 7cm
No prob! so.. SA=Ph
The problem asks for: How much metal is needed to make a CAN to hold three tennis balls?
ohh! LA + 2B
The can is a right circular cylinder with height 21 and a base radius of 7/2. TA = LA + 2B where B is the area of the circular base. TA = 2 pi r h + 2 B TA = 2 pi (7/2) (21) + 2 pi (7/2)^2 TA = 147 pi + 2 pi (49/4) TA = 147 pi + 49/2 pi TA = ( 343 pi) / 2 TA = 538.78 approx = 539 cm (to the nearest cm)
I think you did circumference... 2pir
I forgot what to do with lateral area.. I know its without the bases but just forgot how to use it.
Area of a circle formula --> pi * r^2 The area of one base of the can is pi (7/2)^2. There are two bases; hence, two times the area of one base is 2 pi (7/2)^2. That is the area of the two bases. Lateral area of the cylinder can be found by multiplying the perimeter of the base ( 2 pi r) times the height of the can. I think my work is correct. Check the computations and post here what you think.
That make sense.. I'll just have to review it some more! Thanks for all your help!!!