A cylindrical rod of copper (E = 110 GPa, 16 × 106 psi) having a yield strength of 240 MPa (35,000 psi) is to be subjected to a load of 6660 N (1500 lbf). If the length of the rod is 380 mm (15.0 in.), what must be the diameter to allow an elongation of 0.50 mm (0.020 in.)?

Respuesta :

Answer:

7.65 mm

Explanation:

Stress, [tex]\sigma=\frac {F}{A}[/tex] where F is the force and A is the area

Also, [tex]\sigma=E\times \frac {\triangle L}{L}[/tex]

Where E is Young’s modulus, L is the length and [tex]\triangle L[/tex] is the elongation

Therefore,

[tex]\frac {F}{A}= E\times \frac {\triangle L}{L}[/tex]

Making A the subject of the formula then

[tex]A=\frac {FL}{E\triangle L}=\frac {6660\times 380}{110\times 10^{9}\times 0.5}=4.60145\times 10^{-5} m^{2}[/tex]

Since [tex]A=\frac {\pi d^{2}}{4}[/tex] then  

[tex]d=\sqrt {\frac {4A}{\pi}}=\sqrt {\frac {4\times 4.60145\times 10^{-5}}{\pi}}= 0.00765425m= 7.654249728 mm\approx 7.65 mm[/tex]