High School

The kilogram used to be defined as the mass of a metal cylinder with a height of 39.7 mm and a diameter of 39.4 mm. If we wanted a square prism of the same volume, what length should the sides of the base be if the prism and the cylinder have the same height? Round to the nearest hundredth of a millimeter.

Answer :

The length of the sides of the base should be 39.51 mm.

The formula for the volume of a cylinder is:

[tex]\[ V = \pi r^2 h \][/tex]

Given:

- Height [tex](\(h\))[/tex] = 39.7 mm

- Diameter = 39.4 mm, thus radius [tex](\(r\)) = \(\frac{39.4}{2} = 19.7\)[/tex] mm

Substitute these values into the formula:

[tex]\[ V = \pi (19.7)^2 \cdot 39.7 \][/tex]

[tex]\[ V \approx \pi \cdot 388.09 \cdot 39.7 \][/tex]

[tex]\[ V \approx 48434.06 \, \text{mm}^3 \][/tex]

The formula for the volume of a square prism is:

[tex]\[ V = s^2 h \][/tex]

where [tex]\(s[/tex] is the side length of the base and[tex]\(h\)[/tex]is the height, which is the same for both the cylinder and the square prism.

Given:

- Volume [tex](\(V\))[/tex] = 48434.06 mm³

- Height [tex](\(h\))[/tex] = 39.7 mm

Substitute the known values into the formula:

[tex]\[ 48434.06 = s^2 \cdot 39.7 \][/tex]

Solving for [tex]\(s^2\)[/tex]:

[tex]\[ s^2 = \frac{48434.06}{39.7} \][/tex]

[tex]\[ s^2 \approx 1220.20 \][/tex]

Solving for s:

[tex]\[ s \approx \sqrt{1220.20} \][/tex]

[tex]\[ s \approx 34.93 \, \text{mm} \][/tex]

Therefore, the length of the sides of the base of the square prism should be approximately 34.93 mm.

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