JEE Physics System Of Particles and Rotational Motion MCQs Set B

Question: A thin wire of length l and mass m is bent in the form of a semicircle. The moment of inertia about an axis perpendicular to its plane and passing through the end of the wire is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) 4MR²
• b) 3MR²
• c) 5MR²
• d) 6MR²

Answer:  4MR²

Question:

• a) All of these
• b)  Moment of inertia about an axis passing through one corner and perpendicular to the plane is 2ml²
• c)

  

• d)

  

Answer: All of these

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• d)

  

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Question:

• a) 10 MR²
• b) 4 MR²
• c)

  

• d)

  

Answer: 10 MR²

Question: Two rods of equal lengths(l) and equal mass M are kept along x and y axis respectively such that their centre of mass lie at origin. The moment of inertia about an line y = x, is

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Question: Two rings of same mass and radius R are placed with their planes perpendicular to each other and centres at a common point. The radius of gyration of the system about an axis passing through the centre and perpendicular to the plane of one ring is

• a)

  

• b)

  

• c)

  

• d) 2R

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Question: A thin uniform wire of mass m and length l is bent into a circle. The moment of inertia of the wire about an axis passing through its one end and perpendicular to the plane of the circle is

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• d)

  

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Question: A rod of length L leans against a smooth vertical wall while its other end is on a smooth floor. The end that leans against the wall moves uniformly vertically downward. Select the correct alternative

• a) The speed of the lower end gets smaller and smaller and vanishes when the upper end touches the ground
• b) The speed of the lower end remain constant till upper end touches the ground
• c) The speed of lower end increases at a constant rate
• d) The speed of the lower end decreases but never becomes zero

Answer: The speed of the lower end gets smaller and smaller and vanishes when the upper end touches the ground

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Question: A force F is applied at the centre of a disc of mass M. The minimum value of coefficient of friction of the surface for rolling is

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More Questions..................................

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Question: A rod PQ of mass M and length L is hinged at end P. The rod is kept horizontal by a massless string tied to point Q as shown in figure. When string is cut, the initial angular acceleration of the rod is

• a)

  

• b)

  

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• d)

  

Answer:

Question: A particle undergoes uniform circular motion. About which point in the plane of the circle, will the angular momentum of the particle remain conserved?

• a) Centre of the circle
• b) Inside the circle other than centre
• c) On the circumference of the circle
• d) Outside the circle

Answer: Centre of the circle

Question: When a planet moves around sun, then its

• a) Areal velocity is constant
• b) Linear momentum is conserved
• c) Linear velocity is constant
• d) Angular velocity is constant

Answer: Areal velocity is constant

Question: When a rolling body enters onto a smooth horizontal surface, it will

• a) Continue rolling
• b) Come to rest
• c) Starts slipping
• d) Slipping as well as rolling

Answer: Continue rolling

Question:

• a) All of these
• b) Friction supports rotation motion
• c) Friction opposes its translation
• d)

  

Answer: All of these

Question: A heavy solid sphere is thrown on a horizontal rough surface with initial velocity u without rolling. What will be its speed, when it starts pure rolling motion?

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• b)

  

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Question: A cylinder rolls down two different inclined planes of the same height but of different inclinations

• a) The time of descent will be different but speed will be same
• b) The speed will be different but time of descent will be same
• c) In both cases the speed and time of descent will be same
• d) In both cases the speed and time of descent will be different

Answer: The time of descent will be different but speed will be same

Question: A disc of mass 3 kg rolls down an inclined plane of height 5 m. The translational kinetic energy of the disc on reaching the bottom of the inclined plane is

• a) 100 J
• b) 150 J
• c) 175 J
• d) 50 J

Answer: 100 J

Question: 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) Zero
• b) 0.75 m
• c) 3.0 m
• d) 2.3 m

Answer:  Zero

Question: The centre of mass of a solid cone along the line from the center of the base to the vertex is at

• a) One-fourth of the height
• b) None of these
• c) One-fifth of the height
• d) One-third of the height

Answer: One-fourth of the height

Question: The centre of mass of a system of particles does not depend on

• a) Forces acting on the particles
• b) Relative distances between the particles
• c) Position of the particles
• d) Masses of the particles

Answer: Forces acting on the particles

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• d) d

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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

Answer: 40 cm

Question: Three identical metal balls, each of the 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) Point of intersection of the medians
• b) Centre of one of the balls
• c) Line joining centres of any two balls
• d) Horizontal surface

Answer: Point of intersection of the medians

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Question: A rod of length 3 m has its mass per unit length directly proportional to distance x from one of its ends then its centre of gravity from that end will be at

• a) 2 m
• b) 1.5 m
• c) 2.5 m
• d) 3.0 m

Answer: 2 m

Question: Two particles which are initially at rest, move towards each other under the action of their internal attraction. If their speeds are v and 2v at any instant, then the speed of centre of mass of the system will be

• a) Zero
• b) 1.5 v
• c) 2 v
• d) v

Answer:  Zero

Question: The moment of inertia of a uniform circular disc is maximum about an axis perpendicular to the disc and passing through

• a) B
• b) C
• c) D
• d) A

Answer: B

Question: The moment of inertia of a thin uniform rod of mass M and length L about an axis passing through its midpoint and perpendicular to its length is I₀. Its moment of inertia about an axis passing through one of its ends and perpendicular to its length is

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Question: The ratio of radii of gyration of a circular ring and a circular disc, of the same mass and radius, about an axis passing through their centres and perpendicular to their planes are

• a)

  

• b)

  

• c) 3 : 2
• d) 2 : 1

Answer:

Question: The ratio of the radii of gyration of a circular disc to that of a circular ring, each of same mass and radius, around their respective axes is

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Question: A thin rod of length L and mass M is bent at its midpoint into two halves so that the angle between them is 90^o. The moment of inertia of the bent rod about an axis passing through the bending point and perpendicular to the plane defined by the two halves of the rod is

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Question:   Three particles, each of mass m gram, are situated at the vertices of an equilateral triangle ABC of side l cm (as shown in the figure). The moment of inertia of the system about a line AX perpendicular to AB and in the plane of ABC, in gcm² units will be

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• d)

  

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