PhysicsFlame Institute

(a) Solid sphere will reach the bottom first (b) Hollow spherical shell will reach the bottom first (c) Both will reach at the same time (d) None of these Ans. a (34)

119. Part of the tuning arrangement of a radio consists of a wheel which is acted on by two parallel constant forces as shown in the fig. If the wheel rotates just once, the work done will be about (diameter of the wheel = 0.05m)

(a) 0.062 J (b) 0.031 J (c) 0.015 J (d) 0.057 J Ans. b (31)

120. A solid sphere, a hollow sphere and a ring are released from top of an inclined plane (frictionless) so that they slide down the plane. Then maximum acceleration down the plane is for (no rolling)

(a) Solid sphere (b) hollow sphere (c) Ring (d) All same Ans. d (23)

A body of mass m is placed on the earth’s surface. It is taken from the earth’s surface to a height h=3R . The change in gravitational potential energy of the body is

(a) 2/3 mgR (b) 3/4 mgR (c) mgR/2 (d) mgR/4 Answer: b (5)

Escape velocity of a body of 1 kg mass on a planet is 100 m/sec. Gravitational Potential energy of the body at the Planet is

(a) – 5000 J (b) – 1000 J (c) – 2400 J (d) 5000 J Answer: A (5)

The gravitational potential energy of a body of mass ‘m’ at the earth’s surface -mgRe . Its gravitational potential energy at a height Re from the earth’s surface will be (Here is Re the radius of the earth)

(a) -2 mgR e (b) 2 mgR e (c) 1/2 mgR e (d) -(1/2) mgR e Answer: d (4)

What is the intensity of gravitational field of the centre of a spherical shell

(a) Gm/R2 (b) g (c) Zero (d) None of these Answer: c (10)

There are two bodies of masses 100 kg and 10000 kg separated by a distance 1 m. At what distance from the smaller body, the intensity of gravitational field will be zero

(a) 1/9 m (b) 1/10 m (c) 1/11 m (d) 10/11 m Answer: c (5)

A rocket is launched with velocity 10 km/s. If radius of earth is R, then maximum height attained by it will be

(a) 2R (b) 3R (c) 4R (d) 5R Answer: c (11)

If mass of earth is M, radius is R and gravitational constant is G, then work done to take 1 kg mass from earth surface to infinity will be

(a) √GM/2R (b) GM/R (c) 2√GM/R (d) GM/2R Answer: b (4)

The masses and radii of the earth and moon are M1,R1 and M2,R2 respectively. Their centres are distance d apart. The minimum velocity with which a particle of mass m should be projected from a point midway between their centres so that it escapes to infinity is

answer-a (7)

The change in potential energy, when a body of mass m is raised to a height nR from the earth’s surface is (R = Radius of earth)

(a) mgR n/n-1 (b) nmgR (c) mgR n2/n2+1 (d) mgR n/n+1 Answer: …

The mass of the earth is 6.00 × 10^24 kg and that of the moon is 7.40 × 10^22 kg . The constant of gravitation G=6.67 × 10^-11 N-M^2/kg^2. The potential energy of the system is -7.79 × 10^28 joules . The mean distance between the earth and moon is

(a) 3.80×108 metres (b) 3.37 ×106 metres (c) 7.60×104 metres (d) 1.90×102 metres Answer: a (43)

117. A uniform thin rod of length l is suspended from one of its ends and is rotated at f rotations per second. The rotational kinetic energy of the rod will be

(a) 2/3π2f2ml2 (b) 4/3 f2ml2 (c) 4π2f2ml2 (d) Zero Ans. a (19)

116. If L, M and P are the angular momentum, mass and linear momentum of a particle respectively which of the following represents the kinetic energy of the particle when the particle rotates in a circle of radius R

(a) L2/2M (b) P2/2MR (c) L2/2MR2 (d) MP/2 Ans. c (10)

115. A fly wheel of moment of inertia I is rotating at n revolutions per sec. The work needed to double the frequency would be

(a) 2π2 In2 (b) 4π2 In2 (c) 6π2 In2 (d) 8π2 In2 Ans. c (34)

114. A wheel of radius r rolls without slipping with a speed v on a horizontal road. When it is at a point A on the road, a small jump of mud separates from the wheel at its highest point B and drops at point C on the road. The distance AC will be

(a) v√r/g (b) 2v√r/g (c) 4v√r/g (d) √3r/g Ans. c (18)

113. An engine develops 100 kW, when rotating at 1800 rpm. Torque required to deliver the power is

(a) 531 N–m (b) 570 N–m (c) 520 N–m (d) 551 N–m Ans. a (4)

110. If the rotational kinetic energy of a body is increased by 300% then the percentage increase in its angular momentum will be

(a) 600% (b) 150% (c) 100% (d) 1500% Ans. c (7)

A tangential force F is applied on a disc of radius R, due to which it deflects through an angle θ from its initial position. The work done by this force would be

(a) FR (b) Fθ (c) FR/θ (d) FRθ Ans. d (25)

108. If a body completes one revolution in Π sec then the moment of inertia would be

(a) Equal to rotational kinetic energy (b) Double of rotational kinetic energy (c) Half of rotational kinetic energy (d) Four times the rotational kinetic energy Ans. c (17)