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Physics NEET MCQ
Gravitation Mcq
Quiz 12
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Q.1
Starting from the centre of the earth having radius R, the variation of g ( acceleration due to gravity) is shown by …[ NEET II – 2016]
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a)
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b)
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c)
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d)
Explanation
Answer:(d)
Q.2
A satellite of mass m is orbiting the earth(of radius R) at a height h from its surface. The totalenergy of the satellite in terms of g0, the value ofacceleration due to gravity at the earth's surface, is …[ NEET II – 2016]
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a)
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b)
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c)
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d)
Explanation
Answer:(c)
Q.3
The acceleration due to gravity at a height 1 kmabove the earth is the same as at a depth d belowthe surface of earth. Then …[NEET 2016]
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a) ½ m
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b) 1 km
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c) 3/2 km
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d) 2 km
Explanation
Acceleration due to gravity above earth Acceleration due to gravity below earth given g'=g" d =2h Given h = 1 km ∴ d = 2km Answer:(d)
Q.4
Which of the following statements are correct? …[NEET 2017] (i) Centre of mass of a body always coincides withthe centre of gravity of the body. (ii) Centre of mass of a body is the point at whichthe total gravitational torque on the body is zero (iii) A couple on a body produce both translationaland rotational motion in a body. (iv) Mechanical advantage greater than one meansthat small effort can be used to lift a large load.
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a) (ii) and (iv)
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b) (i) and (ii)
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c) (ii) and (iii)
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d) (iii) and (iv)
Explanation
Statement i is wrong Centre of mass may or may not coincide with centreof gravity. Statement iii is wrong: couple is equal and opposite force produce only rotational motion Answer:(a)
Q.5
Two astronauts are floating in gravitational free spaceafter having lost contact with their spaceship. Thetwo will … [ NEET 2017]
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a) Keep floating at the same distance between them
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b) Move towards each other
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c) Move away from each other
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d) Will become stationary
Explanation
Both the astronauts are in the condition ofweightless. Gravitational force between them pulls towards each other. Answer:(b)
Q.6
Consider a drop of rain water having mass 1 g fallingfrom a height of 1 km. It its the ground with a speedof 50 m/s. Take g constant with a value10 m/sThe work done by the (i) gravitational force and the (ii) resistive force of air is
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a) (i) – 10 J (ii) –8.25 J
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b) (i) 1.25 J (ii) –8.25 J
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c) (i) 100 J (ii) 8.75 J
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d) (i) 10 J (ii) –8.75 J
Explanation
Work done by gravitational force = potential energy of drop W =mgh = 10-3×10×103 = 10 J Work done by resistive force WR= P.E. – K.E of drop when it reach surface WR = 10 – 1.250 = 8.75. This work is done by resistive force so Work is negative = -8.75 J Answer:(d)
Q.7
What is the minimum energy required to launch a satellite of mass m from the surface of a planetof mass M and radius R in a circular orbit at an altitude of 2R ?
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a)
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b)
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c)
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d)
Explanation
Potential energy at surface Potential energy at altitude 2R Kinetic energy of orbiting satellite at altitude 2R Thus total energy at altitude 2R = U+K Kinetic energy to be supplied = Energy at 3R – Energy at surface Answer:(a)
Q.8
then one correct answer Q169) Two bodies, each of mass M, are kept fixed with a separation 2L. A particle of mass m isprojected from the midpoint of the line joining their centres, perpendicular to the line. Thegravitational constant is G. The correct statement(s) is (are) … [ IIT Advance 2013]
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a) The minimum initial velocity of the mass m to escape the gravitational field of the two bodies is
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b) The minimum initial velocity of the mass m to escape the gravitational field of the two bodies is
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c) The minimum initial velocity of the mass m to escape the gravitational field of the twobodies is
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d) The energy of the mass m remains constant
Explanation
Binding energy of mass m This much kinetic energy should be provided to free the body b correct d correct, since gravitational field is conservative. Answer:(b, d)
Q.9
A planet of radius R =X/10 , (X radius of Earth) has the same mass density as Earth. Scientists dig a well of depth R/5 on it and lower a wire of the same length and of linearmass density 10−3 kgm−1 into it. If the wire is not touching anywhere, the force applied atthe top of the wire by a person holding it in place is (take the radius of Earth = 6 × 106 m and the acceleration due to gravity on Earth is 10 ms−2) [IIT Advance 2014]
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a) 96 N
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b) 108 N
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c) 120 N
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d) 150 N
Explanation
R= 6×105 Fore on surface is maximum and as we go down force is reduced. Also as wire goes down the well mass of wire also increases If λ is mass per unit length then mass of the small element lowered wire is λdr. Gravitational force depends up on mass of the sphere at depth ∴ df=λdr×g' F = 1.08×102=108N Answer:(b)
Q.10
A rocket is launched normal to the surface of the Earth, away from the Sun, along the line joining the sun and the Earth. The Sun is 3 × 105 times heavier than the Earth and is at a distance 2.5 ×104 times larger than the radius of the Earth. The escape velocity from Earth's gravitational field is ve = 11.2 km s–The minimum initial velocity (vs) required for the rocket to be able to leave the Sun- Earth system is closest to (Ignore the rotation and revolution of the Earth and the presence of any other planet) [IIT Advance 2017]
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a) vs = 22 km s–1
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b) vs = 72 km s–1
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c) vs = 42 km s–1
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d) vs = 62 km s–1
Explanation
Binding energy Answer:(c)
0 h : 0 m : 1 s
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