Page 101 - Physics - XI

Q8. If force, velocity, and area are considered as a fundamental physical quantity, then fi nd the
dimensional formula of Young’s modulus of elasticity.
a. Y = F v A b. Y = F v A –1/2 c. Y = F v A d. Y = F v A 1/2
–1 1
–1
1 0
1 –1
1 1
1/2
Q9. Steel ruptures when a shear of 3.5 × 10 Nm is applied. This force needed to punch a 1 cm
8
–2
diameter hole in a steel sheet 0.3 cm thick is nearly
a. 1.4 × 10 N b. 2.7 × 10 N c. 3.3 × 10 N d. 1.1 × 10 N
4
4
4
4
Q10. In materials like aluminium and copper, the correct order of magnitude of various elastic
moduli is
a. Young's modulus < shear modulus < bulk modulus
b. Bulk modulus < shear modulus < Young's modulus
c. Shear modulus < Young's modulus < bulk modulus
d. Bulk modulus < Young's modulus < shear modulus
Answer key

1. (b), 2. (c), 3. (b), 4. (b), 5. (d), 6. (c), 7. (d), 8. (a), 9. (c), 10. (c)

Assertion-Reason Type Questions

These consist of two statements– Assertion (A) and Reason (R). Answer these questions by selecting
the appropriate option given below:

a. Both A and R are true and R is the correct explanation of A.
b. Both A and R are true and R is not the correct explanation of A.
c. A is true but R is false.

d. A is false but R is true.

1. Assertion(A) : Silver is an example of a ductile material.
Reason(R) : For a ductile material, yield point and breaking point are separated by a larger
distance than for a brittle material on stress-strain curve.
2. Assertion(A) : Modulus of rigidity of a liquid is zero.

Reason(R) : Shearing stress is also called tangential stress.

3. Assertion(A) : Young's modulus of water is larger than that of steel.
Reason(R) : The extension in the wire is proportional to the length of the wire within elastic
limit.

4. Assertion(A) : Steel is more elastic than rubber.
Reason(R) : Steel can withstand greater stress than rubber.

5. Assertion(A) : The S.I. unit of Young's modulus is same as S.I. unit of stress.
Reason(R) : Strain is dimensionless.

Answer key

1. (a), 2. (b), 3. (d), 4. (a), 5. (a)

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