# Engineering Physics Questions and Answers – Stress and Strain

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Stress and Strain”.

1. If the stress is S and the Young’s modulus is Y of material of a wire, the energy stored in the wire per unit volume is?
a) 2Y/S
b) S/2Y
c) 2S2 Y
d) S2/ 2Y

Explanation: Elastic potential energy stored per unit volume,
u=1/2×Stress×Strain=1/2×Stress×Stress/Y=S2/2Y.

2. Two wires have the same material and have the same volume. However wire 1 had cross sectional area A and wire 2 has cross sectional area 3A. If the length of wire 1 increases by ∆x on applying force F, how much force is needed to stretch wire 2 by the same amount?
a) F
b) 4F
c) 6F
d) 9F

Explanation: Y=F/A l/∆l=F/A2 Al/∆x=FV/(A2 ∆x)
F=Y∆x/V A2
FαA2
F=(3A)2
F/F=9
F=9F.

3. Amorphous solids are true solids.
a) True
b) False

Explanation: Amorphous solids have disordered arrangement of atoms or molecules. The molecules of the liquid are free to move but the molecules of an amorphous solid are almost fixed at their positions. That is why we say amorphous solids are super-cooled liquids of high velocity.

4. An example of a perfectly plastic body is ___________
a) Quartz
b) Crystal
c) Putty
d) Rubber

Explanation: If on the removal of deforming force, a body does not regain its original configuration even a little, then it is said to be a perfectly plastic body. This putty is a perfectly plastic body.

5. No material is perfectly elastic.
a) True
b) False

Explanation: All materials undergo a change in their original state, howsoever small it may be, after the removal of deforming force. Hence, there is no such material that is perfectly elastic.
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6. A given quantity if an ideal gas is at pressure P and absolute temperature T. What is the isothermal bulk modulus of the gas?
a) 2P/3
b) P
c) 3P/2
d) 2P

Explanation: Isothermal bulk modulus of a gas = Pressure of the gas = P.

7. A wire fixed at the upper end stretches by length l by applying a force F. What is the work done in stretching?
a) F/2l
b) Fl
c) 2Fl
d) Fl/2

Explanation: W = 1/2 Stretching force×increase in length
W = 1/2 Fl.

8. The term liquid crystal refers to a state that is intermediate between ___________
a) Crystalline solid and amorphous liquid
b) Crystalline solid and vapour
c) Amorphous liquid and its vapour
d) A crystal immersed in a liquid

Explanation: Liquid crystal is a state intermediate between crystalline solid and amorphous liquid.

9. Which of the following have well defined geometrical external shapes?
a) Amorphous solids
b) Liquids
c) Gases
d) Crystalline solids

Explanation: Crystalline solids have well defined geometrical external shapes because the atoms and molecules are arranged in a definite geometrical repeating manner throughout the body of the crystal.

10. A body of weight mg is hanging on a string that extends in length by l. The work done in extending the string is ___________
a) mgl
b) mgl/2
c) 2mgl
d) 0

Explanation: W=Average force × extension
W=1/2 F×l=1/2 mg×l=mgl/2.

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