Question

1.A brass wire 80 cm long and 0.3 cm in diameter is used to hang an object weighing 6.5 x 10 ^5 dynes. Find stress, strain and young's modules.

2. To one end of a wire 1.2 m long and 0.4 cm in diameter is hung on object with a mass of 10 kg. The wire is found to be elongate 1.34 x 10^4m. Calculate stress, strain and young's modules.

Answer 1

Stress
= force/area

1.
stres= 6.5*10^5 dynes / (π(0.3)²/4 cm²)
= 9195619 dynes/cm²
= 919.6 kPa
Young's modulus nor strain cannot be derived from the given information.

2.
Stress = force /area
10 kg * 9.8 m/s² ÷ (π0.004²/4 m²)
= 7.80 mPa
strain
=Elongation / original length
=1.34*10^(-4) m / 1.2 m (check typo)
=1.12 * 10^(-4)

Young's modulus
= stress/strain
= 7.8 *10^6 / (1.12*10^(-4))
= 6.96*10^10 Pa
= 69.6 GPa (corresponds to that of aluminium)