EP015 PHYSICS 1 1

Tutorial 11

Deformation of Solids

Given : 1 atm = 1.013 x105 Pa

1. A copper wire (Ycopper = 120 GPa) and a tungsten wire (Ytungsten = 360 GPa) are

dimensionally identical. The length and the diameter of the wires are 15.0 m and 5.0

mm. If the wires respectively hang a load of mass 20.0 kg.

a) Determine the stress of both wires.

b) Determine the elongation of copper and tungsten.

c) Determine the strain of both wires.

d) Determine the percentage of elongation of both wire.

e) Which wire is harder?

f) Determine the ratio of elongation of copper to that of tungsten.

g) Sketch the graph of force against elongation for the both wires.

h) Sketch the graph of stress against strain for the both wires.

i) Determine the strain energy of both wires.

j) Determine the strain energy per unit volume of both wires.

2. A solid brass sphere (Bulk modulus = 80 GPa) of radius 50 cm is initially under

atmospheric pressure. The sphere is lowered into the ocean to a depth at which the

pressure is 2.0 x107 Nm-2. Determine :

a) the volume change once the sphere is submerged.

b) the new volume of the sphere.

Suggested Answers

1. (a) copper = tungsten = 10.0 x106 N m-2

(b) xcopper = 1.25 mm, xtungsten = 0.42 mm

(c) copper = 8.3 x10-5, tungsten = 2.8 x10-5

(d) %copper = 0.0083%, %tungsten = 0.0028%

(f) 3

(i) Ucopper = 0.12 J, Utungsten = 0.04 J

(j) U/Vcopper = 1.41x10-4 Jm-3, U/Vtungsten = 4.71x10-5 Jm-3

2. (a) V = -1.29 x10-4 m3

(b) V = 0.5199 m3