NCERT Solutions for Exercise 10.4 Class 12 Maths Chapter 10 - Vector Algebra

NCERT Solutions for Exercise 10.4 Class 12 Maths Chapter 10 - Vector Algebra

Edited By Ramraj Saini | Updated on Dec 04, 2023 09:00 AM IST | #CBSE Class 12th

NCERT Solutions For Class 12 Maths Chapter 10 Exercise 10.4

NCERT Solutions for Exercise 10.4 Class 12 Maths Chapter 10 Vector Algebra are discussed here. These NCERT solutions are created by subject matter expert at Careers360 considering the latest syllabus and pattern of CBSE 2023-24. NCERT solutions for exercise 10.4 Class 12 Maths chapter 10 discuss the questions related to cross product of vectors and their applications. Exercise 10.4 Class 12 Maths have 12 questions. All these 12 questions of NCERT solutions for Class 12 Maths chapter 10 exercise 10.4 are explained with all necessary steps. The Class 12 Maths chapter 10 exercise 10.4 solutions are designed by a mathematics expert and are in accordance with Class 12 CBSE patterns. Concepts of cross products are also explained in Class 11 NCERT Physics TextBooks in the chapter system of particles and rotational motion and are used in other chapters of Class 11 and 12 too. One question may be expected from the Class 12 Maths chapter 10 exercise 10.4 for Class 12 CBSE Class 12 Board Exam.

12th class Maths exercise 10.4 answers are designed as per the students demand covering comprehensive, step by step solutions of every problem. Practice these questions and answers to command the concepts, boost confidence and in depth understanding of concepts. Students can find all exercise together using the link provided below.

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Vector Algebra C lass 12 Chapter 10 Exercise 10.4

Question:1 Find |\vec a \times \vec b |, if \vec a = \hat i - 7 \hat j + 7 \hat k \: \: and \: \: \vec b = 3 \hat i - 2 \hat j + 2 \hat k

Answer:

Given in the question,

\\ \vec a = \hat i - 7 \hat j + 7 \hat k \: \: and \: \: \\\vec b = 3 \hat i - 2 \hat j + 2 \hat k

and we need to find |\vec a \times \vec b |

Now,

|\vec a \times \vec b | =\begin{vmatrix} \hat i &\hat j &\hat k \\ 1 &-7 &7 \\ 3& -2 &2 \end{vmatrix}

|\vec a \times \vec b | =\hat i(-14+14)-\hat j(2-21)+\hat k(-2+21)

|\vec a \times \vec b | =19\hat j+19\hat k

So the value of |\vec a \times \vec b | is 19\hat j+19\hat k

Question:2 Find a unit vector perpendicular to each of the vector \vec a + \vec b \: \: and\: \: \vec a - \vec b , where \vec a = 3 \hat i + 2 \hat j + 2 \hat k \: \:and \: \: \vec b = \hat i + 2 \hat j - 2 \hat k

Answer:

Given in the question

\vec a = 3 \hat i + 2 \hat j + 2 \hat k \: \:and \: \: \vec b = \hat i + 2 \hat j - 2 \hat k

\vec a + \vec b =3\hat i +2\hat j+2\hat k+\hat i +2\hat j-2\hat k=4\hat i +4\hat j

\vec a - \vec b =3\hat i +2\hat j+2\hat k-\hat i -2\hat j+2\hat k=2\hat i +4\hat k

Now , A vector which perpendicular to both \vec a + \vec b \: \: and\: \: \vec a - \vec b is (\vec a + \vec b) \times (\vec a - \vec b)

(\vec a + \vec b) \times (\vec a - \vec b)=\begin{vmatrix} \hat i &\hat j &\hat k \\ 4&4 &0 \\ 2& 0& 4 \end{vmatrix}

(\vec a + \vec b) \times (\vec a - \vec b)= \hat i (16-0)-\hat j(16-0)+\hat k(0-8)

(\vec a + \vec b) \times (\vec a - \vec b)= 16\hat i -16\hat j-8\hat k

And a unit vector in this direction :

\vec u =\frac{16\hat i-16\hat j-8\hat k}{|16\hat i-16\hat j-8\hat k|}=\frac{16\hat i-16\hat j-8\hat k}{\sqrt{16^2+(-16)^2+(-8)^2}}

\vec u =\frac{16\hat i-16\hat j-8\hat k}{24}=\frac{2}{3}\hat i-\frac{2}{3}\hat j-\frac{1}{3}\hat k

Hence Unit vector perpendicular to each of the vector \vec a + \vec b \: \: and\: \: \vec a - \vec b is \frac{2}{3}\hat i-\frac{2}{3}\hat j-\frac{1}{3}\hat k .

Question:3 If a unit vector \vec a makes angles \frac{\pi }{3} with \hat i , \frac{\pi }{4} with \hat j and an acute angle \theta \: \: with \hat k then find \theta \: \: and hence, the components of \vec a .

Answer:

Given in the question,

angle between \vec a and \hat i :

\alpha =\frac{\pi}{3}

angle between \vec a and \hat j

\beta =\frac{\pi}{4}

angle with \vec a and \hat k :

\gamma =\theta

Now, As we know,

cos^2\alpha+cos^2\beta+cos^2\gamma=1

cos^2\frac{\pi}{3}+cos^2\frac{\pi }{4}+cos^2\theta=1

\left ( \frac{1}{2} \right )^2+\left ( \frac{1}{\sqrt{2}} \right )^2+cos^2\theta=1

cos^2\theta=\frac{1}{4}

cos\theta=\frac{1}{2}

\theta=\frac{\pi}{3}

Now components of \vec a are:

\left ( cos\frac{\pi}{3},cos\frac{\pi}{2},cos\frac{\pi}{3} \right )=\left ( \frac{1}{2},\frac{1}{\sqrt{2}},\frac{1}{2} \right )

Question:4 Show that ( \vec a - \vec b ) \times (\vec a + \vec b ) = 2 ( \vec a \times \vec b )

Answer:

To show that ( \vec a - \vec b ) \times (\vec a + \vec b ) = 2 ( \vec a \times \vec b )

LHS=

\\( \vec a - \vec b ) \times (\vec a + \vec b )=( \vec a - \vec b ) \times (\vec a)+( \vec a - \vec b ) \times (\vec b)

( \vec a - \vec b ) \times (\vec a + \vec b )= \vec a \times \vec a-\vec b \times\vec a+\vec a \times \vec b-\vec b \times \vec b

As product of a vector with itself is always Zero,

( \vec a - \vec b ) \times (\vec a + \vec b )= 0-\vec b \times\vec a+\vec a \times \vec b-\0

As cross product of a and b is equal to negative of cross product of b and a.

( \vec a - \vec b ) \times (\vec a + \vec b )= \vec a \times\vec b+\vec a \times \vec b

( \vec a - \vec b ) \times (\vec a + \vec b )= 2(\vec a \times\vec b) = RHS

LHS is equal to RHS, Hence Proved.

Question:5 Find \lambda and \mu if ( 2 \hat i + 6 \hat j + 27 \hat k ) \times ( \hat i + \lambda j + \mu \hat k ) = \vec 0

Answer:

Given in the question

( 2 \hat i + 6 \hat j + 27 \hat k ) \times ( \hat i + \lambda j + \mu \hat k ) = \vec 0

and we need to find values of \lambda and \mu

\begin{vmatrix} \hat i &\hat j & \hat k\\ 2& 6&27 \\ 1& \lambda &\mu \end{vmatrix}=0

\hat i (6\mu-27\lambda)-\hat j(2\mu-27)+\hat k(2\lambda-6)=0

From Here we get,

6\mu-27\lambda=0

2\mu-27=0

2\lambda -6=0

From here, the value of \lambda and \mu is

\lambda = 3 , \: and \: \mu=\frac{27}{2}

Question:6 Given that \vec a . \vec b = 0 \: \:and \: \: \vec a \times \vec b = 0 and . What can you conclude about the vectors \vec a \: \:and \: \: \vec b ?

Answer:

Given in the question

\vec a . \vec b = 0 and \vec a \times \vec b = 0

When \vec a . \vec b = 0 , either |\vec a| =0,\:or\: |\vec b|=0,\vec a\: and \:\vec b are perpendicular to each other

When \vec a \times \vec b = 0 either |\vec a| =0,\:or\: |\vec b|=0,\vec a\: and \:\vec b are parallel to each other

Since two vectors can never be both parallel and perpendicular at same time,we conclude that

|\vec a| =0\:or\: |\vec b|=0

Question:7 Let the vectors \vec a , \vec b , \vec c be given as \vec a_1 \hat i + \vec a_2 \hat j + \vec a_3 \hat k , \vec b_ 1 \hat i + \vec b_ 2 \hat j + \vec b_3 \hat k , \vec c_ 1 \hat i + \vec c_ 2 \hat j + \vec c_ 3 \hat k Then show that \vec a \times ( \vec b + \vec c ) = \vec a \times \vec b + \vec a \times \vec c

Answer:

Given in the question

\\\vec a=\vec a_1 \hat i + \vec a_2 \hat j + \vec a_3 \hat k , \\\vec b=\vec b_ 1 \hat i + \vec b_ 2 \hat j + \vec b_3 \hat k , \\\vec c=\vec c_ 1 \hat i + \vec c_ 2 \hat j + \vec c_ 3 \hat k

We need to show that \vec a \times ( \vec b + \vec c ) = \vec a \times \vec b + \vec a \times \vec c

Now,

\vec a \times ( \vec b + \vec c ) =(\vec a_1 \hat i + \vec a_2 \hat j + \vec a_3 \hat k)\times(\vec b_ 1 \hat i + \vec b_ 2 \hat j + \vec b_3 \hat k +\vec c_ 1 \hat i + \vec c_ 2 \hat j + \vec c_ 3 \hat k)

=(\vec a_1 \hat i + \vec a_2 \hat j + \vec a_3 \hat k)\times((\vec b_ 1+\vec c_1) \hat i + (\vec b_ 2+\vec c_2) \hat j +( \vec b_3 +\vec c_3)\hat k)

=\begin{vmatrix} \hat i &\hat j &\hat k \\ a_1&a_2 &a_3 \\ (b_1+c_1)&(b_2+c_2) &(b_3+c_3) \end{vmatrix}

\\=\hat i(a_2(b_3+c_3)-a_3(b_2+c_2))-\hat j(a_1(b_3+c_3)- a_3(b_1+c_1))+\hat k (a_1(b_2+c_2)-a_2(a_1(b_2+c_3)))

\\=\hat i(a_2(b_3+c_3)-a_3(b_2+c_2))-\hat j(a_1(b_3+c_3)-a_3(b_1+c_1))+\hat k (a_1(b_2+c_2)-a_2(a_1(b_2+c_3)))

Now

\vec a \times \vec b + \vec a \times \vec c=\begin{vmatrix} \hat i &\hat j & \hat k\\ a_1&a_2 &a_3 \\ b_1&b_2 &b_3 \end{vmatrix}+\begin{vmatrix} \hat i &\hat j & \hat k\\ a_1&a_2 &a_3 \\ c_1&c_2 &c_3 \end{vmatrix}

\vec a \times \vec b + \vec a \times \vec c=\hat i(a_2b_3-a_3b_2)-\hat j (a_1b_3-a_3b_1)+\hat k(a_1b_2-b_1a_2)+\hat i(a_2c_3-a_3c_2)-\hat j (a_1c_3-a_3c_1)+\hat k(a_1c_2-c_1a_2)

\\=\hat i(a_2(b_3+c_3)-a_3(b_2+c_2))-\hat j(a_1(b_3+c_3)-a_3(b_1+c_1))+\hat k (a_1(b_2+c_2)-a_2(a_1(b_2+c_3)))

Hence they are equal.

Question:8 If either \vec a = \vec 0 \: \: or \: \: \vec b = \vec 0 then \vec a \times \vec b = \vec 0 . Is the converse true? Justify your answer with an example.

Answer:

No, the converse of the statement is not true, as there can be two non zero vectors, the cross product of whose are zero. they are colinear vectors.

Consider an example

\vec a=\hat i +\hat j + \hat k

\vec b =2\hat i +2\hat j + 2\hat k

Here |\vec a| =\sqrt{1^2+1^2+1^2}=\sqrt{3}

|\vec b| =\sqrt{2^2+2^2+2^2}=2\sqrt{3}

\vec a \times \vec b=\begin{vmatrix} \hat i &\hat j &\hat k \\ 1&1 &1 \\ 2&2 &2 \end{vmatrix}=\hat i(2-2)-\hat j(2-2)+\hat k(2-2)=0

Hence converse of the given statement is not true.

Question:9 Find the area of the triangle with vertices A(1, 1, 2), B(2, 3, 5) and C(1, 5, 5).

Answer:

Given in the question

vertices A=(1, 1, 2), B=(2, 3, 5) and C=(1, 5, 5). and we need to find the area of the triangle

AB=(2-1)\hat i+(3-1)\hat j+(5-2)\hat k=\hat i+2\hat j+3\hat k

BC=(1-2)\hat i+(5-3)\hat j+(5-5)\hat k=-\hat i+2\hat j

Now as we know

Area of triangle

A=\frac{1}{2}|\vec {AB}\times\vec {BC}|=\frac{1}{2}|(\hat i+2\hat j +3\hat k)\times(-\hat i+2\hat j)|

\\A=\frac{1}{2}\begin{vmatrix} \hat i &\hat j &\hat k \\ 1 &2 &3 \\ -1 &2 &0 \end{vmatrix}=\frac{1}{2}|\hat i(0-6)-\hat j(0-(-3))+\hat k(2-(-2))| \\A=\frac{1}{2}|-6\hat i-3\hat j+4\hat k|

A=\frac{1}{2}*\sqrt{(-6)^2+(-3)^2+(4)^2}=\frac{\sqrt{61}}{2}

The area of the triangle is \frac{\sqrt{61}}{2} square units

Question:10 Find the area of the parallelogram whose adjacent sides are determined by the vectors \vec a = \hat i - \hat j + 3 \hat k and \vec b = 2\hat i -7 \hat j + \hat k .

Answer:

Given in the question

\vec a = \hat i - \hat j + 3 \hat k

\vec b = 2\hat i -7 \hat j + \hat k

Area of parallelogram with adjescent side \vec a and \vec b ,

A=|\vec a\times\vec b|=|(\vec i-\vec j+3\vec k)\times (2\hat i-7\hat j+\hat k)|

A=\begin{vmatrix} \hat i& \hat j & \hat k\\ 1&-1 &3 \\ 2&-7 &1 \end{vmatrix}=|\hat i(-1+21)-\hat j (1-6)+\hat k (-7+2)|

A=|\hat i(20)-\hat j (-5)+\hat k (-5)|=\sqrt{20^2+5^2+(-5)^2}

A=\sqrt{450}=15\sqrt{2}

The area of the parallelogram whose adjacent sides are determined by the vectors \vec a = \hat i - \hat j + 3 \hat k and \vec b = 2\hat i -7 \hat j + \hat k is A=\sqrt{450}=15\sqrt{2}

Question:11 Let the vectors \vec a \: \: and\: \: \vec b be such that |\vec a| = 3 \: \: and\: \: |\vec b | = \frac{\sqrt 2 }{3} , then \vec a \times \vec b is a unit vector, if the angle between is \vec a \: \:and \: \: \vec b

\\A ) \pi /6 \\\\ B ) \pi / 4 \\\\ C ) \pi / 3 \\\\ D ) \pi /2

Answer:

Given in the question,

|\vec a| = 3 \: \: and\: \: |\vec b | = \frac{\sqrt 2 }{3}

As given \vec a \times \vec b is a unit vector, which means,

|\vec a \times \vec b|=1

|\vec a| | \vec b|sin\theta=1

3*\frac{\sqrt{2}}{3}sin\theta=1

sin\theta=\frac{1}{\sqrt{2}}

\theta=\frac{\pi}{4}

Hence the angle between two vectors is \frac{\pi}{4} . Correct option is B.

Question:12 Area of a rectangle having vertices A, B, C and D with position vectors

- \hat i + \frac{1}{2} \hat j + 4 \hat k , \hat i + \frac{1}{2} \hat j + 4 \hat k , \hat i - \frac{1}{2}\hat j + 4 \hat k \: \: and \: \: - \hat i - \frac{1}{2} \hat j + 4 \hat k

(A)1/2

(B) 1

(C) 2

(D) 4

Answer:

Given 4 vertices of rectangle are

\\\vec a=- \hat i + \frac{1}{2} \hat j + 4 \hat k , \\\vec b=\hat i + \frac{1}{2} \hat j + 4 \hat k , \\\vec c= \hat i - \frac{1}{2}\hat j + 4 \hat k \: \: and \: \: \\\vec d= - \hat i - \frac{1}{2} \hat j + 4 \hat k

\vec {AB}=\vec b-\vec a=(1+1)\hat i+(\frac{1}{2}-\frac{1}{2})\hat j+(4-4)\hat k=2\hat i

\vec {BC}=\vec c-\vec b=(1-1)\hat i+(-\frac{1}{2}-\frac{1}{2})\hat j+(4-4)\hat k=-\hat j

Now,

Area of the Rectangle

A=|\vec {AB}\times\vec {BC}|=|2\hat i \times (-\hat j)|=2

Hence option C is correct.

More About NCERT Solutions for Class 12 Maths Chapter 10 Exercise 10.4

Exercise 10.4 Class 12 Maths throughout explains about the cross products. The applications of cross products include finding the area of a triangle, parallelogram etc. Question number 9 of the Class 12th Maths chapter 10 exercise 10.4 is to find the area of a triangle. And questions 10 and 12 of NCERT Solutions for Class 12 Maths chapter 10 exercise 10.4 is to find the area of parallelogram and rectangle respectively.

Also Read | Vector Algebra Class 10 Chapter 10 Notes

Benefits of NCERT Solutions for Class 12 Maths Chapter 10 Exercise 10.4

  • Going through the NCERT syllabus exercise 10.4 Class 12 Maths give more conceptual clarifications about the topics covered just before the exercise.
  • Class 12th Maths chapter 10 exercise 10.4 is designed for a better understanding of the concepts of vector products and their applications.
  • The topics covered under NCERT Solutions for class 12 maths chapter 10 exercise 10.4 will also be useful for the exams like JEE Main also.
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Key Features Of NCERT Solutions for Exercise 10.4 Class 12 Maths Chapter 10

  • Comprehensive Coverage: The solutions encompass all the topics covered in ex 10.4 class 12, ensuring a thorough understanding of the concepts.
  • Step-by-Step Solutions: In this class 12 maths ex 10.4, each problem is solved systematically, providing a stepwise approach to aid in better comprehension for students.
  • Accuracy and Clarity: Solutions for class 12 ex 10.4 are presented accurately and concisely, using simple language to help students grasp the concepts easily.
  • Conceptual Clarity: In this 12th class maths exercise 10.4 answers, emphasis is placed on conceptual clarity, providing explanations that assist students in understanding the underlying principles behind each problem.
  • Inclusive Approach: Solutions for ex 10.4 class 12 cater to different learning styles and abilities, ensuring that students of various levels can grasp the concepts effectively.
  • Relevance to Curriculum: The solutions for class 12 maths ex 10.4 align closely with the NCERT curriculum, ensuring that students are prepared in line with the prescribed syllabus.

Also see-

NCERT Solutions Subject Wise

Subject Wise NCERT Exemplar Solutions

Frequently Asked Questions (FAQs)

1. What are vector quantities?

The quantity that has magnitude and also direction is called a vector quantity.

2. What is the difference between a vector quantity and a scalar quantity?

A scalar quantity has magnitude only whereas a vector quantity has both magnitude and directions.

3. The value of cross products of two parallel vectors is?

The value will be zero since the angle between them is zero. The cross product of two vectors a and b is absin(angle between them). For parallel vectors angle between them is zero. So sin(0)=0.

4. What is the difference between a cross b and b cross a?

The direction of a cross b is opposite to the direction of b cross a. That is (a cross b)=-(b cross a)

5. Is stress a vector quantity?

No, stress is neither a vector nor a scalar. Stress is known as a tensor quantity.

6. What do you mean by a unit vector?

It is a vector with magnitude=1

7. Is the statement” the position of the initial point of equal vectors must be same” true?

No, equal vectors may have different initial points, but the magnitude and directions of equal vectors will be the same. 

8. What is understood from the term “negative of a given vector”?

The negative of a given vector is the vector with the same magnitude but opposite in direction. 

9. How many questions can be expected from vector algebra for the board exam?

Two or three questions from vector algebra can be expected for the CBSE Class 12 Maths board exam.

10. How important is vector algebra for Engineering studies?

Vector algebra is used in almost all branches of engineering. If we consider electrical engineering, vector algebra is used to solve certain electromagnetic, power systems, electrical machines and power electronics problems.

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Hello there! Thanks for reaching out to us at Careers360.

Ah, you're looking for CBSE quarterly question papers for mathematics, right? Those can be super helpful for exam prep.

Unfortunately, CBSE doesn't officially release quarterly papers - they mainly put out sample papers and previous years' board exam papers. But don't worry, there are still some good options to help you practice!

Have you checked out the CBSE sample papers on their official website? Those are usually pretty close to the actual exam format. You could also look into previous years' board exam papers - they're great for getting a feel for the types of questions that might come up.

If you're after more practice material, some textbook publishers release their own mock papers which can be useful too.

Let me know if you need any other tips for your math prep. Good luck with your studies!

It's understandable to feel disheartened after facing a compartment exam, especially when you've invested significant effort. However, it's important to remember that setbacks are a part of life, and they can be opportunities for growth.

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Remember: This is a temporary setback. With the right approach and perseverance, you can overcome this challenge and achieve your goals.

I hope this information helps you.







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If you have uploaded screenshot of your 12th board result taken from CBSE official website,there won,t be a problem with that.If the screenshot that you have uploaded is clear and legible. It should display your name, roll number, marks obtained, and any other relevant details in a readable forma.ALSO, the screenshot clearly show it is from the official CBSE results portal.

hope this helps.

Hello Akash,

If you are looking for important questions of class 12th then I would like to suggest you to go with previous year questions of that particular board. You can go with last 5-10 years of PYQs so and after going through all the questions you will have a clear idea about the type and level of questions that are being asked and it will help you to boost your class 12th board preparation.

You can get the Previous Year Questions (PYQs) on the official website of the respective board.

I hope this answer helps you. If you have more queries then feel free to share your questions with us we will be happy to assist you.

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2.45×10−3 kg

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 6.45×10−3 kg

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Option 1)

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Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

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67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

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0.02

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Option 3)

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If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)

Molality

Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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