NCERT Exemplar: Mechanical Properties of Solids | Physics Class 11 - NEET PDF Download

 Page 1


 
 
                                                                                      
 
 
 Mechanical Properties of Solids 
 
Multiple Choice Questions – I 
1. Modulus of rigidity of ideal liquids is 
(a) infinity. 
(b) zero. 
(c) unity. 
(d) some finite small non-zero constant value. 
Ans: Correct option (b)  
Because since we know from given condition that liquid is ideal, thus it does not 
have frictional force among its layers. Hence, tangential forces are zero since no 
stress is developed there. 
 
2.  The maximum load a wire can withstand without breaking when its length 
is reduced to half of its original length, will 
(a) be double. 
(b) be half. 
(c) be four times. 
(d) remain same. 
Ans: Correct option (d)  
Because Breaking stress 
Breaking force
 =  
Area of crosss ection
 
Page 2


 
 
                                                                                      
 
 
 Mechanical Properties of Solids 
 
Multiple Choice Questions – I 
1. Modulus of rigidity of ideal liquids is 
(a) infinity. 
(b) zero. 
(c) unity. 
(d) some finite small non-zero constant value. 
Ans: Correct option (b)  
Because since we know from given condition that liquid is ideal, thus it does not 
have frictional force among its layers. Hence, tangential forces are zero since no 
stress is developed there. 
 
2.  The maximum load a wire can withstand without breaking when its length 
is reduced to half of its original length, will 
(a) be double. 
(b) be half. 
(c) be four times. 
(d) remain same. 
Ans: Correct option (d)  
Because Breaking stress 
Breaking force
 =  
Area of crosss ection
 
 
 
                                                                                      
As breaking force does not depend on length. Thus, changing the cross section has 
no effect which implies breaking force remain same. 
 
3.  The temperature of a wire is doubled. The Young's modulus of elasticity 
(a) will also double. 
(b) will become four times. 
(c) will remain same. 
(d) will decrease. 
Ans: Correct option (d)  
Because as we know that 
t0
L  =  L (1 + a ) t ? 
t 0 0
L - L  =  a L Lt ? ? ? 
00
stress FL FL
Y  =    =    =  
 strain A A(1 + a ) Lt ??
 
1
Y
t
?
?
  
Thus, when temperature increases then Young’s modules decreases. 
 
4. A spring is stretched by applying a load to its free end. The strain produced 
in the spring is 
(a) volumetric. 
(b) shear. 
(c) longitudinal and shear. 
(d) longitudinal. 
Page 3


 
 
                                                                                      
 
 
 Mechanical Properties of Solids 
 
Multiple Choice Questions – I 
1. Modulus of rigidity of ideal liquids is 
(a) infinity. 
(b) zero. 
(c) unity. 
(d) some finite small non-zero constant value. 
Ans: Correct option (b)  
Because since we know from given condition that liquid is ideal, thus it does not 
have frictional force among its layers. Hence, tangential forces are zero since no 
stress is developed there. 
 
2.  The maximum load a wire can withstand without breaking when its length 
is reduced to half of its original length, will 
(a) be double. 
(b) be half. 
(c) be four times. 
(d) remain same. 
Ans: Correct option (d)  
Because Breaking stress 
Breaking force
 =  
Area of crosss ection
 
 
 
                                                                                      
As breaking force does not depend on length. Thus, changing the cross section has 
no effect which implies breaking force remain same. 
 
3.  The temperature of a wire is doubled. The Young's modulus of elasticity 
(a) will also double. 
(b) will become four times. 
(c) will remain same. 
(d) will decrease. 
Ans: Correct option (d)  
Because as we know that 
t0
L  =  L (1 + a ) t ? 
t 0 0
L - L  =  a L Lt ? ? ? 
00
stress FL FL
Y  =    =    =  
 strain A A(1 + a ) Lt ??
 
1
Y
t
?
?
  
Thus, when temperature increases then Young’s modules decreases. 
 
4. A spring is stretched by applying a load to its free end. The strain produced 
in the spring is 
(a) volumetric. 
(b) shear. 
(c) longitudinal and shear. 
(d) longitudinal. 
 
 
                                                                                      
Ans: Correct option is (c) because when spring is stretched by load then its shape 
and length changes which produces shearing and longitudinal strain. 
 
5. A rigid bar of mass M is supported symmetrically by three wires each of 
length 1. Those at each end are of copper and the middle one is of iron. The 
ratio of their diameters, if each is to have the same tension, is equal to 
(a) 
copper 
iron 
Y
Y
 
(b) 
iron 
copper 
Y
Y
 
(c) 
2
iron 
2
copper 
Y
Y
 
(d) 
iron 
copper 
Y
Y
 
Ans: Correct option is (b)  
Because 
 
2
 Stress FL FL
Y  =    =    =  
 Strain A
D
p 
2
L
L
?
??
?
??
??
 
  
2
4FL
Y  =  
p D L ?
 
  L  =  l 
 Copper iron( ) L L g ? ? ?  
F  =  weight of rod same in both cases 
Page 4


 
 
                                                                                      
 
 
 Mechanical Properties of Solids 
 
Multiple Choice Questions – I 
1. Modulus of rigidity of ideal liquids is 
(a) infinity. 
(b) zero. 
(c) unity. 
(d) some finite small non-zero constant value. 
Ans: Correct option (b)  
Because since we know from given condition that liquid is ideal, thus it does not 
have frictional force among its layers. Hence, tangential forces are zero since no 
stress is developed there. 
 
2.  The maximum load a wire can withstand without breaking when its length 
is reduced to half of its original length, will 
(a) be double. 
(b) be half. 
(c) be four times. 
(d) remain same. 
Ans: Correct option (d)  
Because Breaking stress 
Breaking force
 =  
Area of crosss ection
 
 
 
                                                                                      
As breaking force does not depend on length. Thus, changing the cross section has 
no effect which implies breaking force remain same. 
 
3.  The temperature of a wire is doubled. The Young's modulus of elasticity 
(a) will also double. 
(b) will become four times. 
(c) will remain same. 
(d) will decrease. 
Ans: Correct option (d)  
Because as we know that 
t0
L  =  L (1 + a ) t ? 
t 0 0
L - L  =  a L Lt ? ? ? 
00
stress FL FL
Y  =    =    =  
 strain A A(1 + a ) Lt ??
 
1
Y
t
?
?
  
Thus, when temperature increases then Young’s modules decreases. 
 
4. A spring is stretched by applying a load to its free end. The strain produced 
in the spring is 
(a) volumetric. 
(b) shear. 
(c) longitudinal and shear. 
(d) longitudinal. 
 
 
                                                                                      
Ans: Correct option is (c) because when spring is stretched by load then its shape 
and length changes which produces shearing and longitudinal strain. 
 
5. A rigid bar of mass M is supported symmetrically by three wires each of 
length 1. Those at each end are of copper and the middle one is of iron. The 
ratio of their diameters, if each is to have the same tension, is equal to 
(a) 
copper 
iron 
Y
Y
 
(b) 
iron 
copper 
Y
Y
 
(c) 
2
iron 
2
copper 
Y
Y
 
(d) 
iron 
copper 
Y
Y
 
Ans: Correct option is (b)  
Because 
 
2
 Stress FL FL
Y  =    =    =  
 Strain A
D
p 
2
L
L
?
??
?
??
??
 
  
2
4FL
Y  =  
p D L ?
 
  L  =  l 
 Copper iron( ) L L g ? ? ?  
F  =  weight of rod same in both cases 
 
 
                                                                                      
 
2
1
Y
D
? 
 
2
11
D , D
YY
?? 
  
copper 
iron 
iron copper 
D
Y
  =  
DY
  
 
6. A mild steel wire of length 2L and cross-sectional area A is stretched, well 
within elastic limit, horizontally between two pillars (Figure). A mass m is 
suspended from the mid-point of the wire. Strain in the wire is 
 
(a) 
2
2
x
2l
 
(b) 
l
x
 
Page 5


 
 
                                                                                      
 
 
 Mechanical Properties of Solids 
 
Multiple Choice Questions – I 
1. Modulus of rigidity of ideal liquids is 
(a) infinity. 
(b) zero. 
(c) unity. 
(d) some finite small non-zero constant value. 
Ans: Correct option (b)  
Because since we know from given condition that liquid is ideal, thus it does not 
have frictional force among its layers. Hence, tangential forces are zero since no 
stress is developed there. 
 
2.  The maximum load a wire can withstand without breaking when its length 
is reduced to half of its original length, will 
(a) be double. 
(b) be half. 
(c) be four times. 
(d) remain same. 
Ans: Correct option (d)  
Because Breaking stress 
Breaking force
 =  
Area of crosss ection
 
 
 
                                                                                      
As breaking force does not depend on length. Thus, changing the cross section has 
no effect which implies breaking force remain same. 
 
3.  The temperature of a wire is doubled. The Young's modulus of elasticity 
(a) will also double. 
(b) will become four times. 
(c) will remain same. 
(d) will decrease. 
Ans: Correct option (d)  
Because as we know that 
t0
L  =  L (1 + a ) t ? 
t 0 0
L - L  =  a L Lt ? ? ? 
00
stress FL FL
Y  =    =    =  
 strain A A(1 + a ) Lt ??
 
1
Y
t
?
?
  
Thus, when temperature increases then Young’s modules decreases. 
 
4. A spring is stretched by applying a load to its free end. The strain produced 
in the spring is 
(a) volumetric. 
(b) shear. 
(c) longitudinal and shear. 
(d) longitudinal. 
 
 
                                                                                      
Ans: Correct option is (c) because when spring is stretched by load then its shape 
and length changes which produces shearing and longitudinal strain. 
 
5. A rigid bar of mass M is supported symmetrically by three wires each of 
length 1. Those at each end are of copper and the middle one is of iron. The 
ratio of their diameters, if each is to have the same tension, is equal to 
(a) 
copper 
iron 
Y
Y
 
(b) 
iron 
copper 
Y
Y
 
(c) 
2
iron 
2
copper 
Y
Y
 
(d) 
iron 
copper 
Y
Y
 
Ans: Correct option is (b)  
Because 
 
2
 Stress FL FL
Y  =    =    =  
 Strain A
D
p 
2
L
L
?
??
?
??
??
 
  
2
4FL
Y  =  
p D L ?
 
  L  =  l 
 Copper iron( ) L L g ? ? ?  
F  =  weight of rod same in both cases 
 
 
                                                                                      
 
2
1
Y
D
? 
 
2
11
D , D
YY
?? 
  
copper 
iron 
iron copper 
D
Y
  =  
DY
  
 
6. A mild steel wire of length 2L and cross-sectional area A is stretched, well 
within elastic limit, horizontally between two pillars (Figure). A mass m is 
suspended from the mid-point of the wire. Strain in the wire is 
 
(a) 
2
2
x
2l
 
(b) 
l
x
 
 
 
                                                                                      
(c) 
2
x
l
 
(d) 
2
x
2l
 
Ans: Correct option is (a) because 
l (AO BO) AB ? ? ? ? 
l 2AO 2I 2[AO l] ? ? ? ? ? 
? ?
1
22
2
2 l x 1
??
? ? ?
??
??
 
1
2
2
2
x
21 1 1
l
??
??
??
? ? ?
??
??
??
??
 
 
2 2 2
22
2 1 1 2
22
x x x
ll
l l l
??
? ? ? ? ? ?
??
??