✔ 最佳答案
Volume of the copper sphere
=4/3 x pi x 11^3 - 4/3 x pi x (11-1)^3
= 5324pi/3 - 4000pi/3
=1324pi/3
Let r be the radius of the solid sphere
4/3 x pi x r^3=1324pi/3
r^3=331
r=6.92
the radius of the solid sphere is 6.92 cm
2010-04-28 20:19:06 補充：
To 超凡學生,
How can you find 4.58cm??
I want to know if I did anything wrong....
2010-04-28 21:35:47 補充：
Since copper sphere is hollow ,
The volume of the empty space should be excluded.
When the copper sphere is solid, its volume is 5324pi/3 cm^3
4000pi/3 is the empty space.
So the volume of hollow copper sphere is
5324pi/3 - 4000pi/3
=1324pi/3
2010-04-28 21:39:08 補充：
When the hollow copper sphere is melted and recast into a solid sphere, the volume of the new sphere is equal to the hollow one.
An equation 4/3 x pi x r^3=1324pi/3 is foemed to find out the radius of the new sphere.
(If you still don't understand, just tell me and I can explain once more in Chinese.)
2010-04-30 17:40:58 補充：
a hill path 600m long is drawn on a map of scale 1:20000 by a line 2.4m.Find the average gradient of the path. (I think it should be a line 2.4cm, right?)
2010-04-30 17:41:02 補充：
Draw a right-angled triangle to represent the hill path ,
The hypotenuse is 600m and the base is 2.4cmx20000=48000cm=480m
Let θ be the angle between the hypotenuse and base,
cos θ = 480/600 =0.8
θ = 36.9o (corr to 3 sig. fig.)
the average gradient of the path= tanθ = 0.75
