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A cube 6.0 cm on each side is made of a metal alloy. After you drill a cylindrical hole 2.0 cm in diameter all the way through and perpendicular to one face, you find that the cube weighs 6.60 N. 1. What is the density of the metal? (Include units) \rho =?

2. What did the cube weigh before you drilled the hole in it? (Include units) \omega =?

Respuesta :

To solve this problem it is necessary to apply the concepts related to Newton's second law, the definition of density and the geometric relationships that allow us to find the volume of the figures presented.

For the particular case of the Cube with equal sides its volume is determined by

[tex]V_c = l^3[/tex]

[tex]V_c = 6^3 = 216cm^3[/tex]

In the case of perforated material we have that its volume is given according to the cylindrical geometry, that is to say

[tex]V_d = \pi r^2*l[/tex]

[tex]V_d = \pi (\frac{2}{2})^2*6[/tex]

[tex]V_d = 6\pi cm^3[/tex]

In this way the net volume would be

[tex]\Delta V = V_c-V_d[/tex]

[tex]\Delta V = 216cm^3-6\pi cm^3[/tex]

[tex]\Delta V = 197.15cm^3 = 197.15*10^{-6}m^3[/tex]

We need to find the mass, but we have the Weight and Gravity so from Newton's second Law

[tex]F= mg[/tex]

[tex]m = \frac{F}{g}[/tex]

[tex]m = \frac{6.6}{9.8}[/tex]

[tex]m = 0.673kg[/tex]

PART A) From the relation of density as a unit of mass and volume we have to

[tex]\rho = \frac{m}{V}[/tex]

[tex]\rho = \frac{0.673}{197.15*10^{-6}}[/tex]

[tex]\rho = 3413.64kg/m^3[/tex]

PART B) To find the weight of the cube then we apply the ratio of

[tex]W = mg[/tex]

[tex]W = V\rho g[/tex]

[tex]W = (216*10^{-6})(3413.64)(9.8)[/tex]

[tex]W = 7.22N[/tex]

a. The density of the metal is ρ = 3420 kg/m³

b. The weight of the cube before you drilled the hole in it is 7.24 N

Volume of the cube after drilling the hole

Since the cube has a length L = 6.0 cm, its volume is V = L³

= (6.0 cm)³

= 216 cm³.

Volume of cylindrical hole

Since the hole is a cylinder and has a diameter of d = 2.0 cm and height h = L = 6.0 cm, its volume V' = πd²L/4

= π(2.0 cm)² × 6.0 cm/4

= π × 4.0 cm² × 6.0 cm/4

= π × 1.0 cm² × 6.0 cm

= 6π cm³

= 18.85 cm³

Volume of cube after drilling cylindrical hole

So, the volume of the cube after drilling the cylindrical hole is V" = V - V'

= 216 cm³ - 18.85 cm³

= 197.15 cm³

a. Density of metal

The density of the metal is ρ = 3420 kg/m³

The density of the metal ρ = m/V" where

  • m = mass of cube after drilling hole = W/g where
  • W = weight of cube after drilling hole = 6.60 N and
  • g = acceleration due to gravity = 9.8 m/s² and
  • V" = volume of cube after drilling cylindrical hole = 197.15 cm³ = 197.15 × 10⁻⁶ m³

So, ρ = m/V"

ρ = W/gV"

So, substituting the values of the variables into the equation, we have

ρ = W/gV"

ρ =6.60 N/(9.8 m/s² × 197.15 × 10⁻⁶ m³)

ρ = 6.60 N/1932.07 × 10⁻⁶ m⁴/s²)

ρ = 0.00342 × 10⁶ kg/m³

ρ = 3420 kg/m³

So, the density of the metal is ρ = 3420 kg/m³

b. Weight of the cube before drilling hole

The weight of the cube before you drilled the hole in it is 7.24 N

W = mg  where

  • m = mass of cube before drilling hole = ρV where
  • ρ = density of cube = 3420 kg/m³ and
  • V = initial volume of cube = 216 cm³ = 216 × 10⁻⁶ m³ and
  • g = acceleration due to gravity = 9.8 m/s²

Substituting the values of the variables into the equation, we have

W = ρVg

W = 3420 kg/m³ × 216 × 10⁻⁶ m³ × 9.8 m/s²

W = 7239456 × 10⁻⁶ kgm/s²

W = 7.239456 kgm/s²

W = 7.239456 N

W ≅ 7.24 N

So, the weight of the cube before you drilled the hole in it is 7.24 N

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