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Class 11 Physics Objective Chapter – 7 Systems of Particles and Rotational Motion
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7. Systems of Power and Rotational Motion |
1. The rotational inertia of a rigid body is referred to as its —————.
( a ) Moment of energy
( b ) Moment of force
( c ) Moment of inertia
( d ) Moment of acceleration
Answer: ( c )
2. A body of M.I. 3 kgm² rotating with an angular velocity 2 rad/s has the same K.E. as a mass of 12 kg moving with a velocity of
( a ) 1 m/s
( b ) 2 m/s
( c ) 4 m/s
( d ) 8 m/s
Answer: ( a )
3. A particle performing uniform circular motion has angular momentum L . If its angular frequency is doubled and its kinetic energy halved, then the new angular momentum is
( a ) L/2
( b ) L/4
( c ) 2 L
( d ) 4 L
Ans :- ( b )
4. When a dish containing mercury and water is rotated about a vertical axis, the outer portion of the dish contains :
( a ) Water
( b ) Mercury
( c ) Mixture of water and mercury
( d ) Nothing
Ans :- ( a )
5. Two particles of mass 5 kg and 10 kg respectively are attached to the two ends of a rigid rod of length 1 m with negligible mass. The centre of mass of the system from the 5 kg particle is nearly at a distance of
( a ) 33 cm
( b ) 50 cm
( c ) 67 cm
( d ) 80 cm
Ans :- ( c )
6. The wheel of a car is rotating at the rate of 1200 revolutions per minute. On pressing the accelerator for 10 seconds it starts rotating at 4500 revolutions per minute. The angular acceleration of the wheel is
( a ) 30 radian / second2
( b ) 1880 degrees/ second2
( c ) 40 radian / second2
( d ) 1980 degree/second2
Ans :- ( d )
7. A thin uniform, circular ring is rolling down an inclined plane of inclination 300 without slipping. Its linear acceleration along the inclined plane will be
( a ) g/2
( b ) g/3
( c ) g/4
( d ) 2g/3
Ans :- ( a )
8. When a disc rotates with uniform angular velocity, which of the following is not true?
( a ) the sense of rotation remains the same
( b ) the orientation of the axis of rotation remains the same
( c ) the speed of rotation is non-zero and remains the same
( d ) the angular acceleration is non-zero and remains the same
Ans :- ( d )
9. The motion of a potter’s wheel is an example of
( a ) rolling motion
( b ) rotatory motion
( c ) translatory motion
( d ) precessional motion
Ans:- ( b )
10. If a body is rotating about an axis passing through its centre of mass, angular momentum of the body is directed along its —————–.
( a ) Circumference
( b ) Radius
( c ) Axis of rotation
( d ) None of the option
Ans:- ( c )
11. Moment of inertia depends on
( a ) Distribution of particles
( b ) Mass
( c ) Position of axis of rotation
( d ) All of these
Ans:- ( d )
12. Calculate the M.I. of a thin uniform ring about an axis tangent to the ring and in a plane of the ring, if its M.I. about an axis passing through the centre and perpendicular to plane is 4 kg m².
( a ) 12 kg m²
( b ) 3 kg m²
( c ) 6 kg m²
( d ) 9 kg m²
Ans:- ( c )
13. Two circular discs A and B have equal masses and uniform thickness but have densities r1 and r2 such that r1 > r2. their moment of inertia is
( a ) l1 > l2
( b ) l1 >> l2
( c ) l1 < l2
( d ) l1 = l2
Ans:- ( c )
14. Question. Three masses are placed on the x – axis : 300 g at origin, 500 g at x = 40 cm and 400 g at x = 70 cm. The distance of the centre of mass from the origin is
( a ) 40 cm
( b ) 45 cm
( c ) 50 cm
( d ) 30 cm
Ans:- ( a )
15. A certain bicycle can go up a gentle incline with constant speed when the frictional force of ground pushing the rear wheel is F2 = 4 N. With what force F1 must the chain pull on the sprocket wheel if R1=5 cm and R2 = 30 cm?
( a ) 4 N
( b ) 24 N
( c ) 140 N
( d ) (35/4) N
Ans:- ( b )
16. If a body is rotating about an axis, passing through its centre of mass then its angular momentum is directed along its
( a ) Radius
( b ) Tangent
( c ) Circumference
( d ) Axis of rotation
Ans:- ( d )
17. A ring of radius R slides down an inclined plane and reaches the bottom with speed v. If the radius of the ring is doubled keeping its M.I. constant, the speed at the bottom of the inclined plane will be
( a ) v
( b ) 2v
( c ) √2v
( d ) v/√2
Ans:- ( a )
18. The general motion of a rigid body consists of
( a ) translational motion only
( b ) rotational motion only
( c ) both, translational and rotational motion
( d ) does not include translational and rotational motions
Ans:- ( c )
19. Linear velocities of all the particles of the body in rotational motion is ————-.
( a ) 1
( b ) 0
( c ) Same
( d ) Different
Ans:- ( d )
20. A solid cylinder of mass 20 kg, has length 1 metre and radius 0.5m. then its momentum of inertia in kgm² about its geometrical axis is
( a ) 2.5
( b ) 5
( c ) 1.5
( d ) 3
Ans:- ( a )
21. A particle moves on a circular path with decreasing speed. Choose the correct statement.
( a ) Angular momentum remains constant.
( b ) Acceleration is towards the centre.
( c ) Particle moves on a spiral path with decreasing radius.
( d ) The direction of angular momentum remains constant.
Ans:- ( d )
22. For increasing the angular velocity of an object by 10%, the kinetic energy has to be increased by
( a ) 40%
( b ) 20%
( c ) 10%
( d ) 21%
Ans:- ( d )
23. Three identical metal balls, each of radius r are placed touching each other on a horizontal surface such that an equilateral triangle is formed when centres of three balls are joined. The centre of the mass of the system is located at
( a ) line joining centres of any two balls
( b ) centre of one of the balls
( c ) horizontal surface
( d ) point of intersection of the medians
Ans:- ( a )
24. A sphere of mass 2000 g and radius 5 cm is rotating at the rate of 300 rpm .Then the torque required to stop it in 2p revolutions, is
( a ) 1.6 × 102 dyne cm
( b ) 1.6 × 103 dyne cm
( c ) 2.5 × 104 dyne cm
( d ) 2.5 × 105 dyne cm
Ans:- ( d )
25. The M.I. of uniform circular disc about a diameter is I. its M.I. about an axis perpendicular to its plane passing through a point on its rim will be
( a ) 4
( b ) 6
( c ) 8
( d ) 9
Ans:- ( b )
26. A body is under the action of two equal and oppositely directed forces and the body is rotating with constant acceleration. Which of the following cannot be the separation between the lines of action of the forces?
( a ) zero
( b ) 0.25m
( c ) 0.4m
( d ) 1.0m
Ans:- ( a )
27. A rigid body is one
( a ) the sum of distances of all particles from the axis remains constant
( b ) in which the distance between all pairs of particles remains fixed.
( c ) whose centre of mass follows a parabolic path
( d ) The centre of mass of a body
Ans:- ( b )
28. that deforms and comes back to its original shape after getting deformed
( a ) The centre of mass of a body
( b ) lies inside the body
( c ) lies outside the body always
( d ) lies on the surface of the body always
Ans:- ( c )
29. Which is the wrong relation from the following?
( a ) t = I a
( b ) F = ma
( c ) L = I w
( d ) I = t a
Ans:- ( d )
30. The centre of mass of a body
( a ) lies always on the surface of the body
( b ) lies always inside the body
( c ) may lie within, outside on the surface of the body
( d ) lies always outside the body
Ans:- ( a )
31. Centre of mass of the earth and the moon system lies
( a ) closer to the earth
( b ) closer to the moon
( c ) at the mid-point of line joining the earth and the moon
( d ) cannot be predicted
Ans:- ( a )
32. The centre of mass of system of particles does not depend on
( a ) position of the particles
( b ) relative distances between the particles
( c ) masses of the particles
( d ) forces acting on the particle
Ans:- ( b )
33. A solid sphere of mass M and radius R is pulled horizontally on a sufficiently rough surface as shown in the figure
( a ) The acceleration of the centre of mass is F/M
( b ) The acceleration of the centre of mass is 2 F/3 M
( c ) The friction force on the sphere acts forward
( d ) Both ( b ) and ( c )
Ans:- ( d )
34. Which is the wrong relation from the following?
( a ) t = I a
( b ) F = ma
( c ) L = I w
( d ) I = t a
Ans:- ( d )
35. A merry-go-round, made of a ring-like platform of radius R and mass M, is revolving with angular speed ω. A person of mass M is standing on it. At one instant, the person jumps off the ground, radially away from the centre of the round. The speed of the round afterwards is
( a ) 2ω
( b ) ω
( c ) ω/2
( d ) 0
Ans:- ( a )
36. If a shell at rest explodes, then, the centre of mass of the fragments
( a ) remains at rest.
( b ) Moves along a parabolic path.
( c ) Moves along a straight line.
( d ) moves along an elliptical path.
Ans:- ( a )
37. Centre of mass of an isolated system has a ……………
( a ) Increasing velocity
( b ) Constant velocity
( c ) Decreasing velocity
( d ) None of the option
Ans:- ( b )
38. A solid sphere is rotating in free space. If the radius of the sphere is increased keeping mass same, which one of the following will not be affected?
( a ) Moment of inertia
( b ) Angular momentum
( c ) Angular velocity
( d ) Rotational kinetic energy
Ans:- ( b )
39. The position of centre of mass of a system of particles does not depend upon the
( a ) relative distance between the particles
( b ) position of the particles
( c ) symmetry of the body
( d ) mass of particles
Ans:- ( a )
40. Two rings have their moments of inertia in the ratio 2 : 1 and their diameters are in the ratio 2 : 1. The ratio of their masses will be
( a ) 2 : 1
( b ) 1 : 2
( c ) 1 : 4
( d ) 1 : 1
Ans:- ( b )
41. Two persons of masses 55 kg and 65 kg respectively, are at the opposite ends of a boat. The length of the boat is 3.0 m and weighs 100 kg. The 55 kg man walks up to the 65 kg man and sits with him. If the boat is in still water the center of mass of the system shifts by
( a ) 3.0 m
( b ) 2.3 m
( c ) zero
( d ) 0.75 m
Ans:- ( c )
42. A boy and a man carry a uniform rod of length L, horizontally in such a way that the boy gets 1/4th load. If the boy is at one end of the rod, the distance of the man from the other end is
( a ) L/3
( b ) L/4
( c ) 2 L/3
( d ) 3 L/4
Ans:- ( a )
43. A solid sphere is rotating in free space. If the radius of the sphere is increased keeping mass same, which one of the following will not be affected?
( a ) Moment of inertia
( b ) Angular momentum
( c ) Angular velocity
( d ) Rotational kinetic energy
Ans:- ( b )
44. For which of the following does the centre of mass lie outside the body?
( a ) a pencil
( b ) a shotput
( c ) a dice
( d ) a bangle
Ans:- ( d )
45. A child sits stationary at one end of long trolley moving uniformly with speed v on a smooth horizontal floor. If the child gets up and runs about on the trolley in the forward direction with speed u. The centre of mass of the system (child + trolley) will move with speed
( a ) v
( b ) zero
( c ) u + v
( d ) v / u
Ans:- ( a )
46. Radius of gyration is denoted by ————
( a ) R
( b ) G
( c ) K
( d ) I
Ans:- ( c )
47. A body of M.I. 3 kg m² rotating with an angular velocity 2 rad/s has the same K.E. as a mass of 12 kg moving with a velocity of
( a ) 1 m/s
( b ) 2 m/s
( c ) 4 m/s
( d ) 8 m/s
Ans:- ( a )
48. The motion of the centre of mass depends on
( a ) total external forces
( b ) total internal forces
( c ) None of these
( d ) Both
Ans:- ( a )
49. Angular momentum is
( a ) A scalar
( b ) A polar vector
( c ) A scalar as well as vector
( d ) An axial vector
Ans:- ( d )
50. When a mass is rotating in a plane about a fixed point, its angular momentum is directed along
( a ) a line perpendicular to the plane of rotation
( b ) the line making an angle of 45° to the plane of rotation
( c ) the radius
( d ) the tangent to the orbit.
Ans:- ( a )
