Two objects of different masses falling freely near the surface of moon would
(a) have same velocities at any instant
(b) have different accelerations
(c) experience forces of same magnitude
(d) undergo a change in their inertia
Soln:
Answer is (a) have same velocities at any instant
Explanation:
Acceleration of an object depends on acceleration due to gravity irrespective of its mass. Hence object under free fall have the same velocities.
2. The value of acceleration due to gravity
(a) is same on equator and poles
(b) is least on poles
(c) is least on equator
(d) increases from pole to equator
Soln:
Answer is (c) is least on equator
Explanation:
The value of acceleration due to gravity is least on equator because distance between surface of the earth and its centre is more on equator than in poles.
3. The gravitational force between two objects is F. If masses of both objects are halved without changing distance between them, then the gravitational force would become
(a) F/4
(b) F/2
(c) F
(d) 2 F
Soln:
Answer is (a) F/4
4. A boy is whirling a stone tied with a string in an horizontal circular path. If the string breaks, the stone
(a) will continue to move in the circular path
(b) will move along a straight line towards the centre of the circular path
(c) will move along a straight line tangential to the circular path
(d) will move along a straight line perpendicular to the circular path away from the boy
Soln:
Answer is (c) will move along a straight line tangential to the circular path
Explanation:
At any instance of time object in circular motion tend to be in rectilinear motion. Object keeps on moving due to centripetal force and it moves along a straight line tangential to the circular path when strings breaks.
5. An object is put one by one in three liquids having different densities. The object floats with 12 3 , and 9 11 7 parts of their volumes outside the liquid surface in liquids of densities d1, d2 and d3 respectively. Which of the following statement is correct?
(a) d1> d2> d3
(b) d1> d2< d3
(c) d1< d2> d3
(d) d1< d2< d3
Soln:
Answer is (d) d1< d2< d3
6. In the relation F = G M m/d2, the quantity G
(a) depends on the value of g at the place of observation
(b) is used only when the earth is one of the two masses
(c) is greatest at the surface of the earth
(d) is universal constant of nature
Soln:
Answer is (d) is universal constant of nature
Explanation:
G is called as Newton’s constant. It is the force of gravity on a body. Value of G is 6.66x 10-11 Nm2kg-2
7. Law of gravitation gives the gravitational force between
(a) the earth and a point mass only
(b) the earth and Sun only
(c) any two bodies having some mass
(d) two charged bodies only
Soln:
Answer is (c) any two bodies having some mass
8. The value of quantity G in the law of gravitation
(a) depends on mass of earth only
(b) depends on radius of earth only
(c) depends on both mass and radius of earth
(d) is independent of mass and radius of the earth
Soln:
Answer is (d) is independent of mass and radius of the earth
Explanation:
G is an universal constant hence it is independent of mass and radius of the earth.
9. Two particles are placed at some distance. If the mass of each of the two particles is doubled, keeping the distance between them unchanged, the value of gravitational force between them will be
(a) 14 times
(b) 4 times
(c) 12 times
(d) unchanged
Soln:
Answer is (b) 4 times
10. The atmosphere is held to the earth by
(a) gravity
(b) wind
(c) clouds
(d) earth’s magnetic field
Soln:
Answer is (a) gravity
11. The force of attraction between two unit point masses separated by a unit distance is called
(a) gravitational potential
(b) acceleration due to gravity
(c) gravitational field
(d) universal gravitational constant
Soln:
Answer is (d) universal gravitational constant
Explanation:
F= G x
Here point masses are separated by unit distance
Hence m1, m2 and r = 1
Hence F = G which is a universal constant hence answer is universal gravitational constant
12. The weight of an object at the centre of the earth of radius R is
(a) zero
(b) infinite
(c) R times the weight at the surface of the earth
(d) 1/R2 times the weight at surface of the earth
Soln:
Answer is (a) zero
Explanation:
At the centre of the earth acceleration due to gravity is zero. Since weight is the product of mass and gravity. Weight of the object at the centre of the earth will be zero.
13. An object weighs 10 N in air. When immersed fully in water, it weighs only 8 N. The weight of the liquid displaced by the object will be
(a) 2 N
(b) 8 N
(c) 10 N
(d) 12 N
Soln:
Answer is (a) 2 N
Explanation:
Object of weight displace d by liquid = weight in air- weight in liquid
=10N-8N
= 2N
14. A girl stands on a box having 60 cm length, 40 cm breadth and 20 cm width in three ways. In which of the following cases, pressure exerted by the brick will be
(a) maximum when length and breadth form the base
(b) maximum when breadth and width form the base
(c) maximum when width and length form the base
(d) the same in all the above three cases
Soln:
Answer is (b) maximum when breadth and width form the base
Explanation:
Surface area and pressure are inversely proportional. Pressure will be maximum when surface area is minimum hence the answer is maximum when breadth and width form the base.
15. An apple falls from a tree because of gravitational attraction between the earth and apple. If F1 is the magnitude of force exerted by the earth on the apple and F2 is the magnitude of force exerted by apple on earth, then
(a) F1 is very much greater than F2
(b) F2 is very much greater than F1
(c) F1 is only a little greater than F2
(d) F1 and F2 are equal
Soln:
Answer is (d) F1 and F2 are equal
Explanation:
Netwon’s third law of motion states that for every action there is equal and opposite reaction. Hence F1 and F2 are equal.
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