# Need help involving converting units in differentiation questionWatch

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#1
Heres the question:

A spherical ice ball is melting and it has been observed that the radius is decreasing at 1mm per second. Find the volume of the melting water formed in one second when the radius of the sphere is 7cm.

I tried doing this question in two ways,

first converting all my units into mm (i.e 7cm = 70mm), and then working out the answer to be 61575.216 mm^2

then I tried doing the question again, but this time, making sure all my relevant figures were in cm (keeping 7cm, but changing 1mm into 0.1cm). But I worked out the answer to be 61.575216cm^2

1mm^2 = 0.01 cm^2, right?

so surely I should get the same answer bv dividing my first answer (61575.216) by 100. But that doesn't happen, the figure I get is still 10 times bigger than it should be

where have I gone wrong?
0
5 years ago
#2
(Original post by fuzzybear)
Heres the question:

A spherical ice ball is melting and it has been observed that the radius is decreasing at 1mm per second. Find the volume of the melting water formed in one second when the radius of the sphere is 7cm.

I tried doing this question in two ways,

first converting all my units into mm (i.e 7cm = 70mm), and then working out the answer to be 61575.216 mm^2

then I tried doing the question again, but this time, making sure all my relevant figures were in cm (keeping 7cm, but changing 1mm into 0.1cm). But I worked out the answer to be 61.575216cm^2

1mm^2 = 0.01 cm^2, right?

so surely I should get the same answer bv dividing my first answer (61575.216) by 100. But that doesn't happen, the figure I get is still 10 times bigger than it should be

where have I gone wrong?
I think it may because when u calculate in volume, the unit are mm^3 or cm^3
0
#3
(Original post by bird in water)
I think it may because when u calculate in volume, the unit are mm^3 or cm^3
thanks man
0
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