**MCQ of System of Particles and Rotational Motion, Chapter 7, Class 11, Physics**

**Multiple Choice Questions of System of Particles and Rotational Motion, Chapter 7, Class 11, Physics**

**Question 1 : Which of the following is the most appropriate statement about the centre of mass ?**

- The centre of mass always lies at the geometrical centre
- The centre of mass always lie inside the body
- The centre of mass always lie outside the body
- The centre of mass may lie within or outside the body

**Answer : D ( The centre of mass may lie within or outside the body )**

**Question 2 : What will be the position of centre of mass of a cube of uniform density**

- The centre of mass will be at the centre of one face
- Centre of mass will be at the centre of interaction of diagonals of one face
- The position of centre of mass will be at the geometric centre of the cube
- The position of centre of mass will be at the edge of a cube

**Answer : C ( The position of centre of mass will be at the geometric centre of the cube )**

**Question 3 : Two particles are having masses m and 2 m respectively. Then what will be the value of reduced mass of the two particles ?**

- The reduced mass of two particles is 2 m
- The reduced mass of two particles is 3 m
- The reduced mass of two particles is 2 m / 3
- The reduced mass of two particles is m / 2

**Answer : C ( The reduced mass of two particles is 2 m / 3 )**

**Question 4 : A rigid body is said to be in partial equilibrium if it is in**

- When it is in translational equilibrium only
- When it is in rotational equilibrium only
- Both a and b
- Neither a nor b

**Answer : C ( Both a and b )**

**Question 5 : A solid cylinder of radius R and mass M rolls on an inclined plane which is making an angle θ with the horizontal then calculate its acceleration**

- Acceleration is 1/3 g sinθ
- Acceleration is 2/3 g sinθ
- Acceleration is 2/5 g sinθ
- Acceleration is 2/7 g sinθ

**Answer B ( Acceleration is 2/3 g sinθ )**

**Question 6 : In the above question , how much force of friction is acting on the cylinder**

- Force of friction acting on cylinder is 2/3 Mg sinθ
- Force of friction acting on cylinder is 1/3 Mg sinθ
- Force of friction acting on cylinder is 2/5 Mg sinθ
- Force of friction acting on cylinder is 2/7 Mg sinθ

**Answer : B ( Force of friction acting on cylinder is 1/3 Mg sinθ )**

**Question 7 : Which of the following statement is inappropriate about rolling motion ?**

- During rolling motion , the instantaneous velocity of point if contact is negligible
- During rolling motion , the instantaneous acceleration of point if contact is negligible
- During rolling motion , work done against friction is negligible
- If a wheel is moving down on an ideal frictionless surface , the wheel will slip only , but not roll on the floor .

**Answer : B ( During rolling motion , the instantaneous acceleration of point if contact is negligible )**

**Question 8 : A body of mass M is rolling down an inclined plane which is making an angle of 60° with the horizontal . If the kinetic energy of rotation is equals to the 40% of kinetic energy in translatory state than the body is**

- It is a ring
- It’s a cylinder
- It is a hollow ball
- It is a solid ball

**Answer : D ( It is a solid ball )**

**Question 9 : Which of the following statements is mistaken about the rolling motion**

- Torque is the analogue of force in rotational motion
- Rolling motion of a cylinder down an inclined plane which is making an angle O with the horizontal is a combination of rotational motion and the translational motion
- If the effort arm is larger than the load arm then the mechanical advantage is smaller than 1
- For a extended body , centre of mass and centre of gravity do not overlap each other

**Answer : C ( If the effort arm is larger than the load arm then the mechanical advantage is smaller than 1 )**

**Question 10 : A solid sphere rolls down two different inclined planes of same height but the angle of inclination is different for both of the inclined planes then in both cases**

- The speed and time of rolling down in both the cases will be same
- The speed of rolling down the same but the time of this will be different.
- The speed will be different but the time of rolling down will be same
- The speed and time will be different in both the cases

**Answer : B ( The speed of rolling down the same but the time of this will be different.)**

**You may also read MCQ of Physical World, MCQ of Units and Measurements, MCQ of Motion in a Straight Line, MCQ of Motion in a Plane, MCQ of Laws of Motion, MCQ of Work, Energy and Power, MCQ of Gravitation for better understanding of the chapters.**

**Question 11 : Where the angular momentum will be directed if an object of mass M is rotating about a fixed point**

- Angular momentum is directed along the radius
- Angular momentum is directed along the tangent of the orbit
- Angular momentum is directed along the line at angle of 45° to the plane of rotation
- Angular momentum is directed along the axis of rotation

**Answer : D ( Angular momentum is directed along the axis of rotation )**

**Question 12 : What will be the amount of next torque acting on a body if that angular momentum of a rotating body is conserved**

- Net torque is zero
- Net torque is maximum
- Net torque is minimum
- Net torque is unity

**Answer : A ( Net torque is zero )**

**Question 13 : If a flying wheel is rotating at a frequency of 420 rpm slows down at a constant rate of rad s ^{-1} then how much time is required to stop that flying wheel ?**

- 22 s
- 11 s
- 44 s
- 12 s

**Answer : A ( 22 s )**

**Question 14 : Which is the correct analogue of mass in rotational motion**

- Moment of inertia is the analogue of mass in rotational motion
- Torque is the analogue of mass in rotational motion
- Radius of gyration is the analogue of mass in rotational motion
- Angular momentum is analogue of mass in rotational motion

**Answer : A ( Moment of inertia is the analogue of mass in rotational motion )**

**Question 15 : Which of the following quantities the moment of inertia depends on**

- Moment of inertia depends on the mass of body
- Moment of inertia depends on the axis of rotation of the body
- Moment of inertia depends on the shape and size of the body
- All the three

**Answer : D ( All the three )**

**Question 16 : Which of the following materials has the highest moment of inertia if each of them has the same radius ‘r’ and mass ‘m’ ?**

- A Ring has the highest moment of inertia about any of its diameter
- A disc has the highest moment of inertia about any of its diameter
- A hollow sphere about any of its diameter has the highest moment of inertia
- A solid sphere about any of its diameter has the highest moment of inertia

**Answer : C ( A hollow sphere about any of its diameter has the highest moment of inertia )**

**Question 17 : A person is having metals spheres in his hand and is standing on a rotating table if he withdraws his hand to his chest then what will be the effect on the angular velocity ?**

- Angular velocity increases
- Angular velocity decreases
- Angular velocity remain same
- Can’t say

**Answer : A ( Angular velocity increases )**

**Question 18 : 1. Center of gravity is the side at which the weight of a body acts**

**2. If the earth is assumed to have infinite large radius then the centre of mass coincide with the centre of gravity**

**3. To calculate the gravitational field intensity due to body and any external point the entire body can be considered to be concentrated at centre of gravity.**

**4. The radius of gyration is the length of perpendicular drawn from the centre of gravity of the body to axis**

**Which of the following statements are correct ?**

- (1) and (4)
- (1) and (2)
- (2) and (3)
- (3) and (4)

**Answer : A ( (1) and (4) )**

**Question 19 : What is the value of radius of gyration of a uniform rod of length L about an axis passing through one of its end and which is perpendicular to its length**

- L/√2
- L/3
- L/√3
- L/2

**Answer : C ( L/√3 )**

**Question 20 : Which is also known as moment of couple**

- Angular momentum is also known as moment of couple
- Force is also known as moment of couple
- Torque is also known as moment of couple
- Impulse is also known as moment of couple

**Answer : C ( Torque is also known as moment of couple )**

**Question 21 : A moment of couple produces**

- A couple produces a purely translation motion
- A couple produces a purely rotational motion
- A couple produces both translational and rotational motion
- No motion is produced by a couple

**Answer : B ( A couple produces a purely rotational motion )**

**Question 22 : Which of the following statement is incorrect about the equilibrium of a rigid body**

- A couple is a pair of equal and opposite forces with different lines of action
- A couple produces only rotational motion without translational motion
- A certain amount of couple is supplied when we open the lid of a bottle by turning it
- Moment of couple depends on the site about which we take the moment

**Answer : D ( Moment of couple depends on the site about which we take the moment )**

**Question 23 : Why is the angular momentum of a particle rotating with a central force is constant ?**

- It is due to constant torque
- It is due to constant force
- It is due to constant linear momentum
- It is due to zero torque

**Answer : D ( It is due to zero torque )**

**Question 24 : When does the velocity of centre of mass of the system remains constant**

- If the total external force acting on the system is minimum
- If the total external force acting on the system is maximum
- If the total external force acting on the system is unity
- If the total external force acting on the system is zero

**Answer : D ( If the total external force acting on the system is zero )**

**Question 25 : What is the direction of angular velocity vector**

- The direction of angular velocity vector is along the tangent to the circular path
- The direction of angular velocity vector is along the inward radius
- The direction of angular velocity vector is along the outward radius
- The direction of angular velocity vector is along the axis of rotation

**Answer : D ( The direction of angular velocity vector is along the axis of rotation )**

**Question 26 : Which of the following statements is appropriate about the linear velocity and the angular velocity ?**

- Linear momentum and velocity need not to be parallel for a general translational motion
- Angular momentum and angular velocity are always parallel for a general rotational motion
- Acceleration and velocity are always parallel for a general translational motion
- Angular momentum and angular velocity and need not to be parallel four a general rotational motion

**Answer : D ( Angular momentum and angular velocity and need not to be parallel four a general rotational motion )**

**Question 27 : An explosive shell travelling in a parabolic path suddenly explodes in the mid air then where will the centre of mass of the fragments move**

- The centre of mass of the fragments will move in vertically downwards direction
- The centre of mass of the fragments will move along the original parabolic path
- The centre of mass of the fragments will move in vertically upwards and then vertically downward direction .
- The centre of mass of the fragments will move horizontally , followed by the parabolic path

**Answer : B ( The centre of mass of the fragments will move along the original parabolic path )**

**Question 28 : Which of the following will be constant if it torque acting on a system is zero**

- Force will be constant
- Linear impulse will be constant
- Linear momentum will be constant
- Angular momentum will be constant

**Answer : D ( Angular momentum will be constant )**

**Question 29 : What will be the angular momentum w.r.t origin of an object of mass M moving with a constant velocity parallel to X – axis ?**

- Angular momentum is zero
- Angular momentum remains constant
- Angular momentum goes on increasing
- Angular momentum goes on decreasing

**Answer : B ( Angular momentum remains constant )**

**Question 30 : Which of the following relations is appropriate ?**

- Mechanical advantage = Effort / Load
- Load arm × Effort = Effort arm × Load
- Load arm × Load = Effort arm × Effort
- None of these

**Answer : C ( Load arm × Load = Effort arm × Effort )**

**Question 31 : A person is standing on a spinning stool with outstretched arms , if he suddenly brings his hands down , how will kinetic energy and angular momentum be affected ?**

- Both kinetic energy and angular momentum will increase
- Both kinetic energy and angular momentum remains constant
- Kinetic energy remains constant and angular momentum increases
- Kinetic energy increases but angular momentum remains constant

**Answer : D ( Kinetic energy increases but angular momentum remains constant )**

**Question 32 : The moment of inertia of a body A is I _{A} and the moment of inertia of a body B is I_{B} . If angular momentum of both the bodies is equal , then**

**( Given that the moment of inertia of A is greater than moment of inertia of B )**

- Kinetic energy of A will be equal to the kinetic energy of B
- Kinetic energy of A will be greater than the kinetic energy of B
- Kinetic energy of A will be lesser than the kinetic energy of B
- Kinetic energy of two bodies cannot be compared by a given set data

**Answer : C ( Kinetic energy of A will be lesser than the kinetic energy of B )**

**Question 33 : Three bodies a ring , a solid cylinder and a solid sphere starts from rest and are rolled down from the incline plane without slipping . Given that the radial of all the bodies are identical then which of the following bodies will reach the ground with maximum velocity ?**

- Ring will reach the ground with the maximum velocity
- Solid cylinder will reach the ground with maximum velocity
- Solid sphere will reach the ground with maximum velocity
- All the bodies will reach the ground with same velocity

**Answer : C ( Solid sphere will reach the ground with maximum velocity )**

**Question 34 : A solid sphere of mass M is rolled down without slipping an inclined plane which is making an angle O with the horizontal . If initially the acceleration of the centre of mass is ‘a’ . What will be its acceleration is the same sphere slides without friction ?**

- 7 a/2
- 5 a/2
- 7 a/5
- 5 a/2

**Answer : C ( 7 a/5 )**

**Question 35 : A solid sphere of mass M is rolled down without slipping an inclined plane which is making an angle O with the horizontal . What is the correct relation between O and μr**

- tanθ > 3μr
- tanθ ≤ 3μr
- tanθ < 3μr
- None of these

**Answer : B ( tanθ <= 3μr )**

**Question 36 : Which of the following principles a circus acrobat uses in his performance**

- The circus acrobat uses law of conservation of energy
- The circus acrobat uses law of conservation of linear momentum
- The circus acrobat uses law of conservation of mass
- The circus acrobat uses law of conservation of angular momentum

**Answer : D ( The circus acrobat uses law of conservation of angular momentum )**

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