Rotational Motion: JEE Main Previous Year Questions (2021-2026)

 Page 1


JEE Main Previous Year Questions (2021-2026): 
Rotational Motion  
 
(January 2026) 
 
 
Q1: When the position vector  changes sign as  
which one of the following vector will not flip under sign change?  
(a) Velocity  
(b) Linear momentum  
(c) Acceleration  
(d) Angular momentum  
Ans: (d) 
Sol:  
Vectors are categorized into two types based on their symmetry : 
1. Polar Vectors : These represent actual physical displacements. They flip their sign (direction) 
when the coordinate system is inverted . 
2. Axial Vectors (Pseudo-vectors) : These usually represent rotations or are the result of a cross 
product of two polar vectors. They do not flip their sign under coordinate inversion 
 
Velocity is the rate of change of position:  
Since  changes to  
So, when position vector changes sign then velocity vector also get flipped. 
Momentum is defined as  
Since  flips to  becomes  
So the linear momentum also flips if position vector changes sign. 
Page 2


JEE Main Previous Year Questions (2021-2026): 
Rotational Motion  
 
(January 2026) 
 
 
Q1: When the position vector  changes sign as  
which one of the following vector will not flip under sign change?  
(a) Velocity  
(b) Linear momentum  
(c) Acceleration  
(d) Angular momentum  
Ans: (d) 
Sol:  
Vectors are categorized into two types based on their symmetry : 
1. Polar Vectors : These represent actual physical displacements. They flip their sign (direction) 
when the coordinate system is inverted . 
2. Axial Vectors (Pseudo-vectors) : These usually represent rotations or are the result of a cross 
product of two polar vectors. They do not flip their sign under coordinate inversion 
 
Velocity is the rate of change of position:  
Since  changes to  
So, when position vector changes sign then velocity vector also get flipped. 
Momentum is defined as  
Since  flips to  becomes  
So the linear momentum also flips if position vector changes sign. 
Acceleration is the rate of change of velocity:  
 
So, the acceleration also gets flipped when position vector changes sign. 
Angular momentum is defined by the cross product : 
 
If we apply the sign change : 
 
So, it does not flip. It is an axial vector. Hence, the correct option is (d). 
 
Q2: Two circular discs of radius each 10 cm are joined at their centres by a rod of length 
30 cm and mass 600 gm as shown in figure. 
If the mass of each disc is 600 gm and applied torque between two discs is 43 × 10
5
 
dyne.cm, the angular acceleration of the discs about the given axis AB is ______ rad / s
2
. 
Page 3


JEE Main Previous Year Questions (2021-2026): 
Rotational Motion  
 
(January 2026) 
 
 
Q1: When the position vector  changes sign as  
which one of the following vector will not flip under sign change?  
(a) Velocity  
(b) Linear momentum  
(c) Acceleration  
(d) Angular momentum  
Ans: (d) 
Sol:  
Vectors are categorized into two types based on their symmetry : 
1. Polar Vectors : These represent actual physical displacements. They flip their sign (direction) 
when the coordinate system is inverted . 
2. Axial Vectors (Pseudo-vectors) : These usually represent rotations or are the result of a cross 
product of two polar vectors. They do not flip their sign under coordinate inversion 
 
Velocity is the rate of change of position:  
Since  changes to  
So, when position vector changes sign then velocity vector also get flipped. 
Momentum is defined as  
Since  flips to  becomes  
So the linear momentum also flips if position vector changes sign. 
Acceleration is the rate of change of velocity:  
 
So, the acceleration also gets flipped when position vector changes sign. 
Angular momentum is defined by the cross product : 
 
If we apply the sign change : 
 
So, it does not flip. It is an axial vector. Hence, the correct option is (d). 
 
Q2: Two circular discs of radius each 10 cm are joined at their centres by a rod of length 
30 cm and mass 600 gm as shown in figure. 
If the mass of each disc is 600 gm and applied torque between two discs is 43 × 10
5
 
dyne.cm, the angular acceleration of the discs about the given axis AB is ______ rad / s
2
. 
 
(a) 100 
(b) 22 
(c) 27 
(d) 11 
Ans: (d) 
Sol:  
To find the angular acceleration (a), we use the formula : 
t = I
total
 · a ? a = t / I
total
  
where I
total
 is the total moment of inertia of the assembly about the axis AB.  
The rod has mass M = 600 g and length L = 30 cm . The axis AB is perpendicular to the rod at a 
distance of 10 cm from one end.  
The centre of mass (CM) of the rod is at 15 cm from either end.  
The distance (d) between the axis AB and the CM of the rod is: d = 15 cm - 10 cm = 5 cm. 
Page 4


JEE Main Previous Year Questions (2021-2026): 
Rotational Motion  
 
(January 2026) 
 
 
Q1: When the position vector  changes sign as  
which one of the following vector will not flip under sign change?  
(a) Velocity  
(b) Linear momentum  
(c) Acceleration  
(d) Angular momentum  
Ans: (d) 
Sol:  
Vectors are categorized into two types based on their symmetry : 
1. Polar Vectors : These represent actual physical displacements. They flip their sign (direction) 
when the coordinate system is inverted . 
2. Axial Vectors (Pseudo-vectors) : These usually represent rotations or are the result of a cross 
product of two polar vectors. They do not flip their sign under coordinate inversion 
 
Velocity is the rate of change of position:  
Since  changes to  
So, when position vector changes sign then velocity vector also get flipped. 
Momentum is defined as  
Since  flips to  becomes  
So the linear momentum also flips if position vector changes sign. 
Acceleration is the rate of change of velocity:  
 
So, the acceleration also gets flipped when position vector changes sign. 
Angular momentum is defined by the cross product : 
 
If we apply the sign change : 
 
So, it does not flip. It is an axial vector. Hence, the correct option is (d). 
 
Q2: Two circular discs of radius each 10 cm are joined at their centres by a rod of length 
30 cm and mass 600 gm as shown in figure. 
If the mass of each disc is 600 gm and applied torque between two discs is 43 × 10
5
 
dyne.cm, the angular acceleration of the discs about the given axis AB is ______ rad / s
2
. 
 
(a) 100 
(b) 22 
(c) 27 
(d) 11 
Ans: (d) 
Sol:  
To find the angular acceleration (a), we use the formula : 
t = I
total
 · a ? a = t / I
total
  
where I
total
 is the total moment of inertia of the assembly about the axis AB.  
The rod has mass M = 600 g and length L = 30 cm . The axis AB is perpendicular to the rod at a 
distance of 10 cm from one end.  
The centre of mass (CM) of the rod is at 15 cm from either end.  
The distance (d) between the axis AB and the CM of the rod is: d = 15 cm - 10 cm = 5 cm. 
 
Using the Parallel Axis Theorem : 
 
The axis AB is parallel to the diameter of the discs.  
The moment of inertia of a disc about its diameter is Idia  
For the left disc, distance from axis AB is r1 = 10 cm. 
 
For the right disc, distance from axis AB is r
2
 = 20 cm. 
Page 5


JEE Main Previous Year Questions (2021-2026): 
Rotational Motion  
 
(January 2026) 
 
 
Q1: When the position vector  changes sign as  
which one of the following vector will not flip under sign change?  
(a) Velocity  
(b) Linear momentum  
(c) Acceleration  
(d) Angular momentum  
Ans: (d) 
Sol:  
Vectors are categorized into two types based on their symmetry : 
1. Polar Vectors : These represent actual physical displacements. They flip their sign (direction) 
when the coordinate system is inverted . 
2. Axial Vectors (Pseudo-vectors) : These usually represent rotations or are the result of a cross 
product of two polar vectors. They do not flip their sign under coordinate inversion 
 
Velocity is the rate of change of position:  
Since  changes to  
So, when position vector changes sign then velocity vector also get flipped. 
Momentum is defined as  
Since  flips to  becomes  
So the linear momentum also flips if position vector changes sign. 
Acceleration is the rate of change of velocity:  
 
So, the acceleration also gets flipped when position vector changes sign. 
Angular momentum is defined by the cross product : 
 
If we apply the sign change : 
 
So, it does not flip. It is an axial vector. Hence, the correct option is (d). 
 
Q2: Two circular discs of radius each 10 cm are joined at their centres by a rod of length 
30 cm and mass 600 gm as shown in figure. 
If the mass of each disc is 600 gm and applied torque between two discs is 43 × 10
5
 
dyne.cm, the angular acceleration of the discs about the given axis AB is ______ rad / s
2
. 
 
(a) 100 
(b) 22 
(c) 27 
(d) 11 
Ans: (d) 
Sol:  
To find the angular acceleration (a), we use the formula : 
t = I
total
 · a ? a = t / I
total
  
where I
total
 is the total moment of inertia of the assembly about the axis AB.  
The rod has mass M = 600 g and length L = 30 cm . The axis AB is perpendicular to the rod at a 
distance of 10 cm from one end.  
The centre of mass (CM) of the rod is at 15 cm from either end.  
The distance (d) between the axis AB and the CM of the rod is: d = 15 cm - 10 cm = 5 cm. 
 
Using the Parallel Axis Theorem : 
 
The axis AB is parallel to the diameter of the discs.  
The moment of inertia of a disc about its diameter is Idia  
For the left disc, distance from axis AB is r1 = 10 cm. 
 
For the right disc, distance from axis AB is r
2
 = 20 cm. 
 
So, total moment of inertia is, 
 
 
The nearest integer value is 11 . Hence, the correct option is (d). 
 
Q3: A thin uniform rod (X) of mass M and length L is pivoted at a height (L/3) as shown in 
the figure. The rod is allowed to fall from a vertical position and lie horizontally on the 
table. The angular velocity of this rod when it hits the table top, is ______. (g = 
gravitational acceleration)