PhysicsFlame Institute

27. For a satellite escape velocity is 11 km/s. If the satellite is launched at an angle of 60° with the vertical, then escape velocity will be

(a) 11 km/s (b) 11√ 3 km/s (c) 11/√3 km/s (d) 33 km/s Answer: a (6)

15. Assertion : The apparent weight of a body in an elevator moving with some downward acceleration is less than the actual weight of body. Reason : The part of the weight is spent in producing downward acceleration, when body is in elevator.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not the correct explanation of the assertion. (c) If assertion is …

14. Assertion : A rocket works on the principle of conservation of linear momentum. Reason : Whenever there is a change in momentum of one body, the same change occurs in the momentum of the second body of the same system but in the opposite direction.

13. Assertion : A bullet is fired from a rifle. If the rifle recoils freely, the kinetic energy of rifle is more than that of the bullet. Reason : In the case of rifle bullet system the law of conservation of momentum violates.

12. Assertion : Linear momentum of a body changes even when it is moving uniformly in a circle. Reason : Force required to move a body uniformly along a straight line is zero.

11. Assertion : The work done in bringing a body down from the top to the base along a frictionless incline plane is the same as the work done in bringing it down the vertical side. Reason : The gravitational force on the body along the inclined plane is the same as that along the vertical side.

10. Assertion : A cyclist always bends inwards while negotiating a curve. Reason : By bending, cyclist lowers his centre of gravity.

If the angular speed of the earth is doubled, the value of acceleration due to gravity (g) at the north pole

(a) Doubles (b) Becomes half (c) Remains same (d) Becomes zero Answer: C (60)

Spot the wrong statement :The acceleration due to gravity ‘g’ decreases if

(a) We go down from the surface of the earth towards its centre (b) We go up from the surface of the earth (c) We go from the equator towards the poles on the surface of the earth (d) The …

At the surface of a certain planet, acceleration due to gravity is one-quarter of that on earth. If a brass ball is transported to this planet, then which one of the following statements is not correct

(a) The mass of the brass ball on this planet is a quarter of its mass as measured on earth (b) The weight of the brass ball on this planet is a quarter of the weight as measured on earth …

At what altitude in metre will the acceleration due to gravity be 25% of that at the earth’s surface (Radius of earth = R metre)

(a) 1/4 R (b) R (c) 3/8 R …

60. We have two spheres, one of which is hollow and the other solid. They have identical masses and moment of inertia about their respective diameters. The ratio of their radius is given by

(a) 5:7 (b) 3:5 (c) √3:√5 (d) √3:√7 Ans. c (8)

R is the radius of the earth and ω is its angular velocity and gp is the value of g at the poles. The effective value of g at the latitude λ = 60° will be equal to

(a) gp – 1/4 Rω2 (b) gp – 3/4 Rω2 (c) gp – Rω2 (d) gp + 1/4 Rω2 Answer: …

The diameters of two planets are in the ratio 4 : 1 and their mean densities in the ratio 1 : 2. The acceleration due to gravity on the planets will be in ratio

(a) 1 : 2 (b) 2 : 3 (c) 2 : 1 (d) 4 : 1 Answer: …

At what height over the earth’s pole, the free fall acceleration decreases by one percent (assume the radius of earth to be 6400 km)

(a) 32 km (b) 80 km (c) 1.253 km (d) 64 km Answer: a …

The depth d at which the value of acceleration due to gravity becomes 1/n times the value at the surface, is [R = radius of the earth]

(a) R/N (b) R ( n-1/n ) (c) R/n2 …

The moon’s radius is 1/4 that of the earth and its mass is 1/80 times that of the earth. If g represents the acceleration due to gravity on the surface of the earth, that on the surface of the moon is

(a) g/4 (b) g/5 (c) g/6 (d) g/8 Answer: b (4)

If the earth suddenly shrinks (without changing mass) to half of its present radius, the acceleration due to gravity will be

(a) g/2 (b) 4g (c) g/4 (d) 2g Answer: b (10)

If the earth rotates faster than its present speed, the weight of an object will

(a) Increase at the equator but remain unchanged at the poles (b) Decrease at the equator but remain unchanged at the poles (c) Remain unchanged at the equator but decrease at the poles (d) Remain unchanged at the equator but …

Choose the correct statement from the following : Weightlessness of an astronaut moving in a satellite is a situation of

(a) Zero g (b) No gravity (c) Zero mass (d) Free fall Answer: d (3)

The value of g on the earth’s surface is 980 cm /sec2 . Its value at a height of 64 km from the earth’s surface is

(a) 960.40 cm/sec2 (b) 984.90 cm/sec2 (c) 982.45 cm/sec2 (d) 977.55 cm/sec2 (Radius of the earth R …

A spring balance is graduated on sea level. If a body is weighed with this balance at consecutively increasing heights from earth’s surface, the weight indicated by the balance

(a) Will go on increasing continuously (b) Will go on decreasing continuously (c) Will remain same (d) Will first increase and then decrease Answer: b (9)

Which of the following statements is true

(a) g is less at the earth’s surface than at a height above it or a depth below it (b) g is same at all places on the surface of the earth (c) g has its maximum value at the …

The adjoining figure shows a disc of mass M and radius R lying in the X-Y plane with its centre on X-axis at a distance α from the origin. Then the moment of inertia of the disc about the X-axis is

(a) M(R2/2) (b) M(R2/4) (c) M(R2/4+a2) (d) M(R2/2+a2) Ans.b (39)

The value of ‘g’ at a particular point is 9.8 m/s2 . Suppose the earth suddenly shrinks uniformly to half its present size without losing any mass. The value of ‘g’ at the same point (assuming that the distance of the point from the centre of earth does not shrink) will now be

(a) 4.9 m/sec2 (b) 3.1 m/sec2 (c) 9.8 m/sec2 (d) 19.6 m/sec2 Answer: c (5)

The mass of the earth is 81 times that of the moon and the radius of the earth is 3.5 times that of the moon. The ratio of the acceleration due to gravity at the surface of the moon to that at the surface of the earth is

(a) 0.15 (b) 0.04 (c) 1 (d) 6 Answer: a (10)

The radii of two planets are respectively R1 and R2 and their densities are respectively p1 and p2 . The ratio of the accelerations due to gravity at their surfaces is

(a) g1:g2 = p1/R12: p2/R22 (b) g1:g2 = R1R2 : p1p2 (c) g1:g2 = R1 p2 : R2p1 …

What is the moment of inertia of a square sheet of side l and mass per unit area μ about an axis passing through the centre and perpendicular to its plane

(a) μl2/12 (b) μl2/6 (c) μl4/12 (d) μl4/6 Ans. d (7)

According to the theorem of parallel axes I=Ig+Md2 , the graph between l and d will be

Ans. c (5)

The weight of an object in the coal mine, sea level, at the top of the mountain are W1,W2 and W3 respectively, then

(a) W1 <W2 > W3 (b) W1 =W2 =W3 (c) W1 < W2 < W3 (d) W1 > W2 >W3 Answer: a (12)

If R is the radius of the earth and g the acceleration due to gravity on the earth’s surface, the mean density of the earth is

a) 4πG/3gR (b) 3πR/4 gG (c) 3g/4πRG (d) …

The radius of the earth is 6400 km and g=10 m/ sec2 . In order that a body of 5 kg weighs zero at the equator, the angular speed of the earth is

(a) 1/80 radian/sec (b) 1/400 radian/sec (c) 1/800 radian/sec (d) 1/1600 radian/sec Answer: c (27)

Force of gravity is least at

(a) The equator (b) The poles (c) A point in between equator and any pole (d) None of these Answer: a (9)

If the earth stops rotating, the value of ‘g’ at the equator will

(a) Increase (b) Remain same (c) Decrease (d) None of the above Answer: a (19)

The mass and diameter of a planet have twice the value of the corresponding parameters of earth. Acceleration due to gravity on the surface of the planet is

(a) 9.8 m/sec2 (b) 4.9 m/sec2 (c) 980 m/sec2 …

As we go from the equator to the poles, the value of g

(a) Remains the same (b) Decreases (c) Increases (d) Decreases upto a latitude of 45° Answer: c (11)

56. On account of melting of ice at the north pole the moment of inertia of spinning earth

(a) Increases (b) Decreases (c) Remains unchanged (d) Depends on the time Ans. a (13)

A spherical planet far out in space has a mass M0 and diameter D0 . A particle of mass m falling freely near the surface of this planet will experience an acceleration due to gravity which is equal to

(a) GM0 /D02 (b) 4m GM0 /D02 (c) 4 GM0 /D02 …

In order to find time, the astronaut orbiting in an earth satellite should use

(a) A pendulum clock (b) A watch having main spring to keep it going (c) Either a pendulum clock or a watch (d) Neither a pendulum clock nor a watch Answer: b (7)