PhysicsFlame Institute

(a) Hooke’s law is applicable only within elastic limit (b) The adiabatic and isothermal elastic constants of a gas are equal (c) Young’s modulus is dimensionless (d) Stress multiplied by strain is equal to the stored energy Answer-a (41)

If V, R and g denote respectively the escape velocity from the surface of the earth radius of the earth, and acceleration due to gravity, then the correct equation is

(a) V=√gR (b) V=√ 4/3 gR 3 (c) V = R√g (d) …

The escape velocity for a body projected vertically upwards from the surface of earth is 11 km/s. If the body is projected at an angle of 45o with the vertical, the escape velocity will be

(a) ( 11/√2 )km/s (b) 11√2km/s (c) 22 km/s (d) 11 km/s Answer: d (3)

63. A copper wire and a steel wire of the same diameter and length are connected end to end and a force is applied, which stretches their combined length by 1 cm. The two wires will have

(a) Different stresses and strains (b) The same stress and strain (c) The same strain but different stresses (d) The same stress but different strains Answer-d (11)

62. Which one of the following quantities does not have the unit of force per unit area

(a) Stress (b) Strain (c) Young’s modulus of elasticity (d) Pressure Answer-b (5)

61. Which one of the following substances possesses the highest elasticity

(a) Rubber (b) Glass (c) Steel (d) Copper Answer-c (9)

Escape velocity on the surface of earth is 11.2 km/s . Escape velocity from a planet whose mass is the same as that of earth and radius 1/4 that of earth is

(a) 2.8 km/s (b) 15.6 km/s (c) 22.4 km/s (d) 44.8 km/s Answer: c (12)

65. A wire extends by 1 mm when a force is applied. Double the force is applied to another wire of same material and length but half the radius of cross-section. The elongation of the wire in mm will be

(a) 8 (b) 4 (c) 2 (d) 1 Answer-a (10)

Escape velocity on the earth

(a) Is less than that on the moon (b) Depends upon the mass of the body (c) Depends upon the direction of projection (d) Depends upon the height from which it is projected Answer: d (5)

151. A uniform solid cylinder of mass M and radius R rotates about a frictionless horizontal axle. Two similar masses suspended with the help two ropes wrapped around the cylinder. If the system is released from rest then the acceleration of each mass will be

(a) 4mg/M+2m (b) 4mg/M+4m (c) 2mg/M+m (d) 2mg/M+2m Ans. b (19)

150. A cylinder of mass M and radius r is mounted on a frictionless axle over a well. A rope of negligible mass is wrapped around the cylinder and a bucket of mass m is suspended from the rope. The linear acceleration of the bucket will be

(a) Mg/M+2m (b) 2Mg/m+2M (c) Mg/2M+m (d) 2mg/M+2m Ans. d (85)

149. A massless string is wrapped round a disc of mass M and radius R. Another end is tied to a mass m which is initially at height h from ground level as shown in the fig. If the mass is released then its velocity while touching the ground level will be

(a) √(2gh) (b) √(2gh)M/m (c) √(2ghm/M) (d) √(4mgh/2m+M) Ans. d (65)

148. A uniform disc of radius R and mass M can rotate on a smooth axis passing through its centre and perpendicular to its plane. A force F is applied on its rim. See fig. What is the tangential acceleration

(a) 2F/M (b) F/M (c) F/2M (d) F/4M Ans. a (34)

The escape velocity of a rocket launched from the surface of the earth

(a) Does not depend on the mass of the rocket (b) Does not depend on the mass of the earth (c) Depends on the mass of the planet towards which it is moving (d) Depends on the mass of the …