NEET Previous year questions (2014-2024): System of Particles & Rotational Motion | Physics Class 11 PDF Download

Q3: A disc of radius 2 m and mass 100 kg rolls on a horizontal floor. Its centre of mass has speed of 20 cm/s. How much work is needed to stop it?               [2019]
(a) 1 J
(b) 2 J
(c) 3 J
(d) 30 J
Ans: (c)

Apply the law of conservation of energy,
Work required = change in kinetic energy
Since, final KE = 0

2018

Q1: Three objects, A : (a solid sphere), B : (a thin circular disk) and C = (a circular ring), each have the same mass M and radius R. They all spin with the same angular speed ω about their own symmetry axes. The amounts of work (W) required to bring them to rest, would satisfy the relation:-    [2018]
(a) W_C > W_B > W_A
(b) W_A > W_B > W_C
(c) W_B > W_A > W_C
(d) W_B > W_A > W_C
Ans: (a) 
Solution:

Q2: The moment of the force,  at (2, 0, –3), about the point (2, –2, –2), is given by:-    [2018]
(a)
(b)
(c)
(d)
Ans: (d) 
Solution:

Q3: A solid sphere is in rolling motion. In rolling motion a body possesses translational kinetic energy (Kt) as well as rotational kinetic energy (Kr) simultaneously. The ratio Kt : (Kt + Kr) for the sphere is    [2018]
(a) 7 : 10
(b) 5 : 7
(c) 10 : 7
(d) 2 : 5
Ans: (b) 
Solution:

Q4: A solid sphere is rotating freely about its symmetry axis in free space. The radius of the sphere is increased keeping its mass same. Which of the following physical quantities would remain constant for the sphere ?    [2018]
(a) Angular velocity
(b) Moment of inertia
(c) Rotational kinetic energy
(d) Angular momentum
Ans: (d) 
Solution:

2017

Q1: A rope is wound around a hollow cylinder of mass 3 kg and radius 40 cm. What is the angular acceleration of the cylinder if the rope is pulled with a force of 30 N ?    [2017]
(a) 0.25 rad/s²
(b) 25 rad/s²
(c) 5 m/s²
(d) 25 m/s²
Ans: (b) 
Solution:

Q2: Two discs of same moment of inertia rotating about their regular axis passing through centre and perpendicular to the plane of disc with angular velocities ω₁ and ω₂. They are brought into contact face to face coinciding the axis of rotation. The expression for loss of energy during this process is:-    [2017]
(a)
(b)
(c)
(d)
Ans: (a) 
Solution:

Q3: Which of the following statements are correct ?    [2017]
(a) Centre of mass of a body always coincides with the centre of gravity of the body
(b) Central of mass of a body is the point at which the total gravitational torque on the body is zero
(c) A couple on a body produces both translational and rotation motion in a body
(d) Mechanical advantage greater than one means that small effort can be used to lift a large load
(a) (a) and (b)
(b) (b) and (c)
(c) (c) and (d)
(d) (b) and (d)
Ans: (d) 
Solution: Centre of mass may lie on centre of gravity net torque of gravitational pull is zero about centre of mass.

2016

Q1: From a disc of radius R and mass M₁ a circular hole of diameter R₁ whose rim passes through the centre is cut. What is the moment of inertia of the remaining part of the disc about at perpendicular axis, passing through the centre ?    [2016]
(a) 9MR²/32
(b) 15MR²/32
(c) 13MR²/32
(d) 11 MR²/32
Ans: (c)
Solution:


Option C is correct Answer.

Q2: A disk and a sphere of same radius but different masses roll off on two inclined planes of the same altitude and length. Which one of the two objects gets to the bottom of the plane first ?    [2016]
(a) Depends on their masses
(b) Disk
(c) Sphere
(d) both reach at the same time
Ans: (c) 
Solution: Time does not depend on mass, else

K²/R² is least for sphere and hence least time is taken by sphere

Q3: A uniform circular disc of radius 50 cm at rest is free to turn about an axis which is perpendicular to its plane and passes through its centre. It is subjected to a torque which produces a constant angular acceleration of 2.0 rad s^-2. Its net acceleration in ms^-2 at the end of 2.0 s is approximately :    [2016]
(a) 3.0
(b) 8.0
(c) 7.0
(d) 6.0
Ans: (b) 
Solution: The angular speed of disc increases with time, and hence centripetal acceleration also increases.

Q4: A light rod of length l has two masses m₁ and m₂ attached to its two ends. The moment of inertia of the system about an axis perpendicular to the rod and passing through the centre of mass is       [2016]
(a)

(b)

(c)

(d)

Ans: (a)

Q5: A solid sphere of mass m and radius R is rotating about its diameter. A solid cylinder of same mass and same radius is also rotating about its geometrical axis with an angular speed twice that of the sphere. The ratio of their kinetic energies of rotation (E_sphere / E_cylinder) will be        [2016]
(a) 2 : 3
(b) 1 : 5
(c) 1 : 4
(d) 3 : 1
Ans: (b)

2015

Q1: Three identical spherical shells, each of mass m and radius r are placed as shown in figure. Consider an axis XX' which is touching to two shells and passing through diameter of third shell. Moment of inertia of the system consisting of these three spherical shells about XX' axis is :    [2015]

(a) 4 mr²
(b) 11/5 mr²
(c) 3 mr²
(d) 16/5 mr²
Ans: (a) 
Solution:

Similarly the moment of inertia of the spherical shell C about the XX' axis is

Q2: A rod of weight W is supported by two parallel knife edges A and B and is in equilibrium in a horizontal position. The knives are at a distance d from each other. The centre of mass of the rod is at distance x from A. The normal reaction on A is       [2015]
(a)

(b)

(c)

(d)
Ans: (b)

Given situation is shown in figure.
N₁ = Normal reaction on A
N₂ = Normal reaction on B
W = Weight of the rod
In vertical equilibrium,
N₁ + N₂ = W …(i)
Torque balance about centre of mass of the rod,
N₁x = N₂(d – x)
Putting value of N₂ from equation (i)
N₁x = (W – N₁)(d – x)
$\Rightarrow$ N₁x = Wd – Wx – N₁d + N₁x
$\Rightarrow$ N₁d = W(d – x) 

Q3: Three identical spherical shells, each of mass m and radius r are placed as shown in figure. Consider an axis XX' which is touching to two shells and passing through diameter of third shell. Moment of inertia of the system consisting of these three spherical shells about XX' axis is      [2015]

(a) 16/5mr²
(b) 4mr²
(c) 11/5mr²
(d) 3mr²
Ans: (b)
Net moment of inertia of the system,
I = I₁ + I₂ + I₃
The moment of inertia of a shell about its diameter, 

Q4: An automobile moves on a road with a speed of 54 km h^$-$1. The radius of its wheels is 0.45 m and the moment of inertia of the wheel about its axis of rotation is 3 kg m². If the vehicle is brought to rest in 15 s, the magnitude of average torque transmitted by its brakes to the wheel is 
(a) 10.86 kg m² s^$-$2 
(b) 2.86 kg m² s^$-$2 
(c) 6.66 kg m² s^$-$2 
(d) 8.58 kg m² s^$-$2 
Ans: (c)
Here, Speed of the automobile,

Radius of the wheel of the automobile, R = 0.45 m
Moment of inertia of the wheel about its axis of rotation, I = 3 kg m²
Time in which the vehicle brought to rest, t = 15 s
The initial angular speed of the wheel is 

Q5: A force  is acting at a point . The value of αfor which angular momentum about origin is conserved is       [2015]
(a) Zero
(b) 1
(c) -1
(d) 2
Ans: (c)
From Newton's second law for rotational motion,

2014

Q1: A solid cylinder of mass 50 kg and radius 0.5 m is free to rotate about the horizontal axis. A massless string is wound round the cylinder with one end attached to it and other hanging freely. Tension in the string required to produce an angular acceleration of 2 revolutions s⁻² is:    [2014]
(a) 78.5 N
(b) 157 N
(c) 25 πN
(d) 50 N
Ans: (a) 
Solution:


Q2: The ratio of the accelerations for a solid sphere (mass ‘m’ and radius ‘R’) rolling down an incline of angle ‘θ’ without slipping and slipping down the incline without rolling is :    [2014]
(a) 2 : 5
(b) 7 : 5
(c) 5 : 7
(d) 2 :3
Ans: (c) 
Solution:


Q3: A body of mass (4m) is lying in x−y plane at rest. It suddenly explodes into three pieces. Two pieces, each of mass (m) move perpendicular to each other with equal speeds (ν). The total kinetic energy generated due to explosion is :    [2014]
(a) 2 mν²
(b) 4 mν²
(c) mν²
(d) 3/2 mν²
Ans: (d)
Solution: