A 1000-kg object hangs from the lower end of a steel rod 5.0 m long that is suspended vertically. The diameter of the rod is 0.80 cm and Young's modulus for the rod is 210,000 MN/m2. What is the elongation of the rod due to this object?
A) 0.047 cm
B) 1.2 cm
C) 0.12 cm
D) 1.8 cm
E) 0.46 cm

Respuesta :

Answer:E

Explanation:

Given

mass of object [tex]m=1000 kg[/tex]

Length of steel rod [tex]L=5 m[/tex]

diameter of rod [tex]d=0.8 cm[/tex]

Young modulus [tex]E=210,000 MN/m^2[/tex]

And we know [tex]E=\frac{stress}{strain}[/tex]

[tex]stress=\frac{Load}{Area}[/tex]

[tex]Strain=\frac{\Delta L}{L}[/tex]

Therefore [tex]\Delta =\frac{FL}{AE}[/tex]

[tex]\Delta =\frac{1000\times 9.8\times 5}{\frac{\pi (0.8\times 10^{-2})^2}{4}\times 210000\times 10^6}[/tex]

[tex]\Delta =\frac{20\times 9.8}{\pi \times 0.64\times 210\times 100}[/tex]

[tex]\Delta =4.64\times 10^{-3} m[/tex]

[tex]\Delta =0.464 cm[/tex]

Answer:

[tex]\Delta L=4.642\,mm[/tex]

Explanation:

Given:

mass of the hanging object, m= 1000 kg

original length of the steel rod, L=5 m

diameter of the rod, d= 0.80 cm

Young's modulus for the rod, E = [tex]210,000 MPa[/tex]

Firstly we find the value of stress:

[tex]\sigma = \frac{Force}{area}[/tex]

[tex]\sigma = \frac{1000\times 9.8}{\pi\times 4^2}[/tex]

[tex]\sigma = 194.9648 MPa[/tex]

Now strain,

[tex]\epsilon= \frac{\sigma}{E}[/tex]

[tex]\epsilon= \frac{194.9648 }{210000}[/tex]

[tex]\epsilon= 0.00093[/tex]

We know,

[tex]\epsilon= \frac{\Delta L}{L}[/tex]

[tex]0.00093= \frac{\Delta L}{5000}[/tex]

[tex]\Delta L=4.642\,mm[/tex]