You have bought a kind of paint that could paint 50 m 2 per quart. Then you used approximately 6.28 quarts of paint to color the surface of a sphere. Now you wish to paint a cube that has a side length the same as the sphere's radius. How much paint do you need, in quarts?
(P.S. use 3.14 as an approximation for pi., and m means meter.)
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The sphere's surface area, as implied by the given conditions, is 5 0 × 6 . 2 8 = 3 1 4 m 2 . According to the formula for the surface area of a sphere ( S A = 4 π r 2 ), it is clear that the radius of the sphere is 5 m . Plug in 5 for the surface area formula for cube, and you will get 150 m 2 . This number divided by 50 m 2 would be 3 .
It is given in the problem that 1 q u a r t = 5 0 m 2 . So the surface area of the sphere is 6 . 2 8 q u a r t s converted to m 2 . Convert:
6 . 2 8 q u a r t s ( 1 q u a r t 5 0 m 2 ) = 3 1 4 m 2
Solve for the radius of the sphere by using the formula: s = 4 π r 2 where s is the surface area of the sphere and r is the radius of the sphere. Substitute:
3 1 4 = 4 ( 3 . 1 4 ) r 2 ⟹ r 2 = 2 5 ⟹ r = 5
The formula for the surface area of the cube is 6 a 2 where a is the edge length. Substitute:
A = 6 ( 5 2 ) = 1 5 0 m 2
So the number of quarts needed is 1 5 0 m 2 ( 5 0 m 2 1 q u a r t ) = 3 q u a r t s
The surface area of the sphere is,
S A = 6 . 2 8 q u a r t s ( 1 q u a r t 5 0 m 2 ) = 3 1 4 m 2
4 p i ∗ r 2 = 3 1 4
r = 5
The surface area of the cube is,
S A = 6 ∗ 5 2 = 1 5 0 m 2
1 5 0 m 2 ( 5 0 m 2 1 q u a r t ) = 3 q u a r t s
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let A S be the area of the sphere
by ratio and proportion, we get
6 . 2 8 A S = 1 5 0 ⟹ A S = 3 1 4 m 2
the area of the sphere is given by the formula A S = 4 π r 2 , substituting, we get
3 1 4 = 4 ( 3 . 1 4 ) ( r 2 ) ⟹ r 2 = 2 5 ⟹ r = 5
the surface area of a cube is given by the formula A C = 6 a 2 , but a = r = 5 , substituting, we get
A C = 6 ( 5 2 ) = 6 ( 2 5 ) = 1 5 0 m 2
let N be the number of quarts needed for the cube, then
N = 1 5 0 m 2 ( 5 0 m 2 1 q u a r t ) = 3 q u a r t s