Mechanical Properties of Solids Questions and Answers Part-9

1. An iron rod of length 2m and cross section area of \[50mm^{2}\] , stretched by 0.5 mm, when a mass of 250 kg is hung from its lower end. Young's modulus of the iron rod is
a) \[19.6 \times 10^{10}N\diagup m^{2}\]
b) \[19.6 \times 10^{15}N\diagup m^{2}\]
c) \[19.6 \times 10^{18}N\diagup m^{2}\]
d) \[19.6 \times 10^{20}N\diagup m^{2}\]

Answer: a

2. In solids, inter-atomic forces are
a) Totally repulsive
b) Totally attractive
c) Combination of (a) and (b)
d) None of these

Answer: c
Explanation: Combination of (a) and (b)

3. A force F is applied on the wire of radius r and length L and change in the length of wire is l. If the same force F is applied on the wire of the same material and radius 2r and length 2L, Then the change in length of the other wire is
a) l
b) 2l
c) l/2
d) 4l

Answer: c

4. The modulus of elasticity is dimensionally equivalent to
a) Surface
b) Stress
c) Strain
d) None of these

Answer: b
Explanation: Stress

5. Under elastic limit the stress is
a) Inversely proportional to strain
b) Directly proportional to strain
c) Square root of strain
d) Independent of strain

Answer: b
Explanation: Directly proportional to strain

6. A load W produces an extension of 1mm in a thread of radius r. Now if the load is made 4W and radius is made 2r all other things remaining same, the extension will become
a) 4 mm
b) 16 mm
c) 1 mm
d) 0.25 mm

Answer: c

7. The units of Young ‘s modulus of elasticity are
a) \[ N m^{-1}\]
b) N-m
c) \[ N m^{-2}\]
d) \[ N m^{2}\]

Answer: c
Explanation: \[ N m^{-2}\]

8.Two similar wires under the same load yield elongation of 0.1 mm and 0.05 mm respectively. If the area of cross- section of the first wire is \[ 4mm^{2}\] then the area of cross section of the second wire is
a) \[ 6mm^{2}\]
b) \[ 8mm^{2}\]
c) \[ 10mm^{2}\]
d) \[ 12mm^{2}\]

Answer: b

9. A 5 m long aluminium wire \[\left(Y=7 \times 10^{10}N\diagup m^{2}\right)\]    of diameter 3 mm supports a 40 kg mass. In order to have the same elongation in a copper wire \[\left(Y=12 \times 10^{10}N\diagup m^{2}\right)\]    of the same length under the same weight, the diameter should now be, in mm.
a) 1.75
b) 1.5
c) 2.5
d) 5.0

Answer: c

10. How much force is required to produce an increase of 0.2% in the length of a brass wire of diameter 0.6 mm (Young’s modulus for brass = 0.9 * 1011 N/m2 )
a) Nearly 17 N
b) Nearly 34 N
c) Nearly 51 N
d) Nearly 68 N

Answer: c