NCERT Exemplar Class 12 Biology Solutions Chapter 3 Human Reproduction

NCERT Exemplar Class 12 Biology Solutions Chapter 3 Human Reproduction

Edited By Priyanka kumari | Updated on Aug 25, 2022 06:10 PM IST | #CBSE Class 12th

NCERT exemplar Class 12 Biology solutions chapter 3 Human Reproduction is a very important chapter from the examination point of view. The experts in this field who have deep knowledge and understanding about the field have prepared NCERT exemplar Class 12 Biology chapter 3 solutions to provide accurate information. The experts have used simple and understandable language to prepare Class 12 Biology NCERT exemplar solutions in chapter 3. The solutions will help the students to refer to this quality study material to experience the best learning. NCERT exemplar Class 12 Biology solutions chapter 3 pdf download is useful to access it offline.

In this chapter of NCERT Class 12 Solutions, the students will learn and study the different reproductive events in humans, which include the formation of sperms in males, ovulation in females, insemination, fertilization, implantation, gestation, and the delivery of the baby.

Long Answer Type Questions:

Question:1

What role do pituitary gonadotropins play during follicular and ovulatory phases of the menstrual cycle? Explain the shifts in steroidal secretions.

Answer:

Pituitary gonadotropins (FSH and LH) play a very vital role during the follicular and ovulatory phases of the menstrual cycle.

  • FSH stimulates the release of ovum from the Graafian follicle. It also stimulates the development and subsequent rupture of Graafian follicle. Thus, FSH plays a major role during the follicular and ovulatory phases.
  • The above figure shows varying levels of LH. FSH and steroid hormones during follicular and ovulation phases of the menstrual cycle.
  • At this stage, the level of estradiol (a steroid hormone) increases. This suppresses the level of Luteinizing hormone (LH). Once the level of estradiol reaches a threshold level, the effect is reversed.
  • After that, the level of estrogen (another steroid hormone) increases. This stimulates a surge in levels of LH. High level of L.H stimulates the development of corpus luteum and proliferation of the endometrium, thus, marking the beginning of the luteal phases.

Question:2

Meiotic division during oogenesis is different from that in spermatogenesis. Explain how and why?

Answer:

It is true that the meiotic division during oogenesis is different from that in spermatogenesis. Following are the details about significant differences between them:

  • In the case of spermatogenesis, meiotic division begins at the time of puberty. This is the time when spermatogenesis begins in a male. On the other hand, oogenesis begins in the female when the female is still in the womb. Thus, it can be said that meiotic division during oogenesis begins when the girl child is still in the womb.
  • Formation of primary oocytes stops by the 20th week of gestation of the female child. On the contrary, the production of spermatocytes continues throughout the reproductive phase of a male.
  • All the stages of meiosis take place quickly after one another in case of spermatogenesis and there is no time lag between them. In case of oogenesis, meiosis is deferred at the Prophase I state.

Meiosis resumes only once the puberty begins.
Following are some possible reasons for this difference in patterns of oogenesis and spermatogenesis:

  • Male gametes need to be formed in very large number to ensure Fertilisation.
  • Female gametes are not exposed to external hazards, and hence a less number of them would be enough. Limiting the production of female gametes helps in conservation of resources from the female body. The resources can then be properly utilised during the development of the foetus.

Question:3

The zygote passes through several developmental stages till implantation, Describe each stage briefly with suitable diagrams.

Answer:

The following figure shows various stages of zygote development till implantation:

(a) The zygote divides into two-cell stage called cleavage. This development takes place when the zygote is still in the isthmus.
(b) The cleavage undergoes further rounds of mitosis to form 2, 4, 8 and finally 16-celled stage.
These daughter cells are called blastomere.
(c) The 16-celled stage is known as morula.
(d) The morula changes into blastocyst; with more rounds of meiosis. At this stage, the blastomeres are arranged in an outer layer of cells; called trophoblast and an inner mass of cells.
(e) Implantation to uterine wall happens at the blastocyst stage.

Question:4

Draw a neat diagram of the female reproductive system and label the parts associated with the following
(a) production of gamete,
(b) site of fertilisation
(c) site of implantation and,
(d) birth canal.

Answer:


Question:5

With a suitable diagram, describe the organisation of mammary gland.

Answer:

Mammary glands are paired structures which contain glandular tissue and a variable amount of fat.

  • Glandular tissue present in each breast is made up of 15 - 20 mammary lobes. These lobes have clusters of cells known as alveoli.
  • Milk, stored in the cavities (lumens) of alveoli, is secreted from the cells of alveoli. The alveoli open in mammary tubules.
  • Tubules from each lobe join to form a mammary duct.
  • Many mammary ducts join to form a wider mammary ampulla.
  • A mammary ampulla is connected to the lactiferous duct. Milk is sucked out through the lactiferous duct.

Short Answer Type Questions:

Question:1

A human female experiences two major changes, menarche, and menopause during her life. Mention the significance of both the events.

Answer:

Menarche marks the onset of puberty (beginning of reproductive phase).
Menopause marks the end of the reproductive phase.

Question:2

a. How many spermatozoa are formed from one secondary spermatocyte?

b. Where does the first cleavage division of zygote take place?

Answer:

(a) One secondary spermatocyte forms four spermatids, all of which subsequently develop into spermatozoa via the process spermiogenesis.
(b) The first cleavage division of zygote takes place in the ampullary-isthmus junction.

Question:4

Corpus luteum in pregnancy has a long life. However, if Fertilisation does not take place, it remains active only for 10-12 days. Explain.

Answer:

Corpus luteum is responsible for the secretion of progesterone, which is essential to maintain the endometrium and helps in the proper development of the foetus.
This is the reason for the long life of Corpus luteum when Fertilisation has occurred. However, when there is no fertilisation, it serves no purpose and thus remains active only for 10-12 days

Question:4

What is foetal ejection reflex? Explain how it leads to parturition?

Answer:

Foetal ejection reflex is the mild uterine contraction at the time of childbirth. It triggers the release of oxytocin from the maternal pituitary, which induces strong uterine contraction and finally leads to parturition.

Question:5

Except for the endocrine function, what are the other functions of the placenta?

Answer:

The placenta is responsible for the following in addition to its endocrine function –
(A) Supply of oxygen and nutrient to foetus
(B) Removal of waste products from the foetus

Question:6

Why do doctors recommend breastfeeding during the initial period of infant growth?

Answer:

Milk produced during the initial few days of lactation is known as colostrum and contains several antibodies, which are important for the development of disease resistance in the baby. This is the prime reason why doctors recommend breastfeeding during the initial period of growth of an infant.

Question:7

What are the events that take place in the ovary and uterus during the follicular phase of the menstrual cycle?

Answer:

During the follicular phase of the menstrual cycle, the following things happen in the ovary and the uterus –

  1. The primary follicle in the ovary grows into fully mature Graafian follicle
  2. Endometrium in the uterus regenerates through the proliferation
  3. Estrogen is secreted by growing follicle

Question:8

Given below is a flow chart showing ovarian changes during the menstrual cycle. Fill in the spaces giving the name of the hormones responsible for the events shown.

Answer:

Hormones responsible for various changes during the menstrual cycle are:

  1. Follicle Stimulating Hormone (FSH): It is responsible for the transformation of the primary follicle into Graafian follicle.
  2. Follicle Stimulating Hormone (FSH): It is also responsible for ovulation. It works in coordination with LH and complement its function.
  3. Luteinizing Hormone (LH): It is responsible for the development of corpus luteum from Graafian follicle.

Question:10

What are the changes in the oogonia during the transition of a primary follicle to Graafian follicle?

Answer:

Following changes occur in the oogonia during the transition of a primary follicle to Graafian follicle:
(a) Each primary oocyte is surrounded by a layer of granulosa cells; called a primary follicle
(b) Primary follicle transforms into secondary follicle by getting surrounded by another layer of granulosa cells and a new theca.
(c) The secondary follicle then transforms into the tertiary follicle. The tertiary follicle is characterised by a fluid-filled cavity called the antrum. At this stage, the primary oocyte undergoes second meiotic division and forms secondary oocyte and a tiny polar body.
(d) The tertiary follicle then changes into mature Graafian follicle. During this stage, a new layer; called zona pellucida; develops around the secondary oocyte.

Very Short Answer Type Questions:

Question:1

Given below are the events in human reproduction. Write them in correct sequential order. Insemination, gametogenesis, Fertilisation, parturition, gestation, implantation

Answer:

Gametogenesis→Insemination→Fertilization→Implantation→Gestation→Parturition

Question:3

What is the role of cervix in the human female reproductive system

Answer:

Cervix and vagina together form the birth canal. Parturition happens through the birth canal.

Question:4

Why are menstrual cycles absent during pregnancy?

Answer:

Gonadotropins, which are required for the development of new follicles, are suppressed due to the high levels of progesterone and estrogen during pregnancy. This inhibits the initiation of a new menstrual cycle.

Question:5

Female reproductive organs and associated functions are given below in column A and B. Fill the blank boxes.

Column A
Column B
Ovaries
Oviduct
B
Vagina
Ovulation
A
Pregnancy
Birth


Answer:

A. Fertilisation
B. Uterus

Question:6

From where the parturition signals arise-mother or foetus? Mention the main hormone involved in parturition

Answer:

Parturition signals arise from the foetus. Oxytocin is the main hormone involved in parturition and is released from the maternal pituitary gland.

Question:7

What is the significance of epididymis in male fertility?

Answer:

Secretions from the epididymis, vas deferens, prostate and seminal vesicle are essential for maturation and motility of sperms. These organs play an important role in male fertility.

Question:8

Give the names and functions of the hormones involved in the process of spermatogenesis. Write the names of the endocrine glands from where they are released.

Answer:

Hormone
Function
Hormone’s origin
Gonadotropin Releasing Hormone (GnRH)
Act on the anterior pituitary gland and stimulates the release of LH and FSH
Hypothalamus
Luteinizing Hormone (LH)
Acts at Leydig cells and stimulates the secretion of androgen
Pituitary
Follicle Stimulating Hormone (FSH)
Acts on Sertoli cells and stimulates factors which are involved in spermatogenesis
Pituitary


Question:10

During reproduction, the chromosome number (2n) reduces to half (n) in the gametes, and again the original number (2n) is restored in the offspring, what are the processes through which these events take place?

Answer:

Chromosome number reduces to half in gametes as, during gametogenesis, meiosis takes place resulting in the haploid number of chromosomes.
During Fertilisation, male and female gametes undergo fusion to make the diploid zygote.


Question:11

What is the difference between a primary oocyte and a secondary oocyte?

Answer:

Primary Oocyte
Secondary Oocyte
Primary oocyte is formed when the female is still in the womb
Secondary oocyte is formed when the individual undergoes puberty
It is surrounded by secondary follicle
It is surrounded by tertiary follicle
Number of chromosomes is 46
Number of chromosomes is 23



Question:12

What is the significance of ampullary-isthmic junction in the female reproductive tract?

Answer:

First cleavage division of zygote occurs in the ampullary-isthmic junction in the female reproductive tract

Question:13

How does zona pellucida of ovum help in preventing polyspermy?

Answer:

Zona pellucida’s membrane undergoes changes when sperm comes into contact with it. This prevents the entry of other sperm into the ovum and thus prevent polyspermy.

Question:14

Mention the importance of LH surge during the menstrual cycle.

Answer:

Rupture of Graafian follicle is induced by a rapid surge in LH level. Resulting in the release of ovum (ovulation)

Question:15

Which type of cell division forms spermatids from the secondary spermatocytes?

Answer:

Meiosis results in the formation of spermatids from secondary spermatocytes.

Multiple Choice Questions:

Question:1

Choose the incorrect statement from the following:
a. In birds and mammals, internal Fertilisation takes place
b. Colostrum contains antibodies and nutrients
c. Polyspermy in mammals is prevented by the chemical changes in the egg surface
d. In the human female implantation occurs almost seven days after Fertilisation

Answer:

The answer is the option (c) Polyspermy in mammals is prevented by the chemical changes in the egg surface
Explanation: Zona pellucida absorbs water and swells preventing further entry of sperms. So, physical change rather than chemical change is responsible for the prevention of polyspermy in mammals.

Question:2

Identify the correct statement from the following:
a. High levels of estrogen trigger the ovulatory surge.
b. Oogonial cells start to proliferate and give rise to functional ova in regular cycles from puberty onwards.
c. Sperms released from seminiferous tubules are highly motile.
d. Progesterone level is high during the post-ovulatory phase of the menstrual cycle

Answer:

The answer is the option (d) Progesterone level is high during the post-ovulatory phase of the menstrual cycle
Explanation: Ovulatory surge is triggered by the high levels of LH and FSH. Sperms released from seminiferous tubules are non-motile. Oogonial cells stop their activity when the girl child is still in the womb.

Question:3

Spot the odd one out from the following structures with reference to the male reproductive system:
a. Rete testis
b. Epididymis
c. Vasa efferentia
d. Isthmus

Answer:

The answer is the option (d) Isthmus
Explanation: Isthmus is a part of the oviduct in the female reproductive system. Others are parts of the male reproductive system

Question:4

Seminal plasma, the fluid part of semen, is contributed by.
i. Seminal vesicle
ii. Prostate gland
iii. Urethra
iv. Bulbourethral gland
(a) i and ii (b) i, ii and iv (c) ii, iii and iv (d) i and iv

Answer:

The answer is the option (b) (i), (ii) and (iv)
Explanation: Urethra has no contribution to seminal plasma

Question:5

Spermiation is the process of the release of sperms from:
a. Seminiferous tubules
b. Vas deferens
c. Epididymis
d. Prostate gland

Answer:

The answer is the option (a) Seminiferous tubules
Explanation: Seminiferous tubules

Question:6

Mature Graafian follicle is generally present in the ovary of a healthy human female around:
a. 5 – 8 day of menstrual cycle
b. 11 – 17 day of menstrual cycle
c. 18 – 23 day of menstrual cycle
d. 24 – 28 day of the menstrual cycle

Answer:

The answer is the option (b) 11-17 day of the menstrual cycle
Explanation: After rupturing in Graafian follicle, ovulation takes place in this period

Question:7

The acrosomal reaction of the sperm occurs due to:
a. Its contact with zona pellucida of the ova
b. Reactions within the uterine environment of the female
c. Reactions within the epididymal environment of the male
d. Androgens produced in the uterus

Answer:

The answer is the option (a) Its contact with zona pellucida of the ova
Explanation: Sperm can enter the ova only after the enzyme from acrosome breaks down the zona pellucida

Question:8

Which one of the following is not a male accessory gland?
a. Seminal vesicle
b. Ampulla
c. Prostate
d. Bulbourethral gland

Answer:

The answer is the option (b) Ampulla
Explanation: Ampulla is part of the fallopian tube

Question:9

The spermatogonia undergo division to produce sperms by the process of spermatogenesis. Choose the correct one with reference to above.
a. Spermatogonia have 46 chromosomes and always undergo meiotic cell division
b. Primary spermatocytes divide by mitotic cell division
c. Secondary spermatocytes have 23 chromosomes and undergo second meiotic division
d. Spermatozoa are transformed into spermatids

Answer:

The answer is the option (c) Secondary spermatocytes have 23 chromosomes and undergo second meiotic division
Explanation: Spermatogonia have 46 chromosomes, and they undergo meiotic cell division; primary spermatocytes undergo meiotic cell division. Spertamids and transformed into spermatozoa

Question:10

Match between the following representing parts of the sperm and their functions and choose the correct option.

Column I
A. Head
B. Middle piece
C. Acrosome
D. Tail
Column II
i. Enzymes
ii. Sperm motility
iii. Energy
iv. Genetic material

a. A-ii, B-iv, C-i, D-iii
b. A-iv, B-iii, C-i, D-ii
c. A-iv, B-i, C-ii, D-iii
d. A-ii, B-i, C-iii, D-iv

Answer:

The answer is the option (b) (A) – (iv), (B) – (iii), (C) – (i), (D) – (ii)
Explanation: Nucleus is present in the head. Acrosome releases enzyme which dissolves zona pellucida. The tail helps in swimming of sperm and the middle piece is the place where mitochondria are present

Question:12

Match the following and choose the correct options:

Column I
A. Trophoblast
B. Cleavage
C. Inner cell mass
D. Implantation
Column II
i. Embedding of the blastocyst in the endome
trium
ii. Group of cells that would differentiate
as embryo
iii. The outer layer of blastocyst attached to the
endometrium
iv. Mitotic division of the zygote

a. A-ii, B-i, C-iii, D-iv
b. A-iii, B-iv, C-ii, D-i
c. A-iii, B-i, C-ii, D-iv
d. A-ii, B-iv, C-iii, D-i

Answer:

The answer is the option (b) (A)-(iii), (B)-(iv), (C)-(ii), (D)-(i)

Question:13

Which of the following hormones is not secreted by human placenta?

a. hCG
b. Estrogens
c. Progesterone
d. LH

Answer:

The answer is the option (d) LH
Explanation: LH (Luteinizing hormone) is secreted by the pituitary gland

Question:14

The vas deferens receives duct from the seminal vesicle and opens into urethra as:
a. Epididymis
b. Ejaculatory duct
c. Efferent ductule
d. Ureter

Answer:

The answer is the option (b) Ejaculatory duct
Explanation: Ejaculatory duct

Question:15

Urethral meatus refers to the:
a. Urinogenital duct
b. Opening of vas deferens into urethra
c. The external opening of the urinogenital duct
d. Muscles surrounding the urinogenital duct

Answer:

The answer is the option (c) External opening of the urinogenital duct
Explanation: External opening of the urinogenital duct

Question:16

Morula is a developmental stage:
a. Between the zygote and blastocyst
b. Between the blastocyst and gastrula
c. After the implantation
d. Between implantation and parturition

Answer:

The answer is the option (a) between the zygote and blastocyst
Explanation: between the zygote and blastocyst

Question:17

The membranous cover of the ovum at ovulation is:
a. Corona Radiata
b. Zona radiata
c. Zona pellucida
d. Chorion

Answer:

The answer is the option (a) corona radiate
Explanation: corona radiate

Question:18

Identify the odd one from the following:
a. Labia minora
b. Fimbriae
c. Infundibulum
d. Isthmus

Answer:

The answer is the option (a) Labia Minora

NCERT exemplar Class 12 Biology solutions chapter 3 helps students to learn and understand the different reproductive events, thus they will get to know about the functioning of different parts in a human body.

Major Subtopics in NCERT Exemplar Class 12 Biology Solutions Chapter 3 Human Reproduction:

  • 3.1 The Male Reproductive System
  • 3.2 The Female Reproductive System
  • 3.3 Gametogenesis
  • 3.4 Menstrual Cycle
  • 3.5 Fertilisation and Implantation
  • 3.6 Pregnancy and Embryonic Development
  • 3.7 Parturition and Lactation
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NCERT Exemplar Class 12 Biology Solutions Chapter 3 Human Reproduction - Learning Outcome:

  • In Class 12 Biology NCERT exemplar solutions chapter 3, the students will learn about the different events that take place in the human body with the functioning of reproductive parts.
  • There are different topics that are covered in this chapter that the students should know when it comes to human reproduction. Every topic covered in NCERT exemplar Class 12 Biology chapter 3 solutions is very well explained in detail.
  • The students will study the various reproductive events that occur after puberty in humans. There are many differences between the reproductive events occurring in males and females.
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NCERT Exemplar Class 12 Biology Chapter Wise Links:

Benefits of NCERT Exemplar Class 12 Biology Solutions Chapter 3 Human Reproduction:

  • The different parts and how they function in the human body is very important for the students to understand. The reproductive parts and their functioning is very well explained in the NCERT exemplar solutions for Class 12 Biology chapter 3.
  • It also provides important information about the different stages and how it is developed.
  • NCERT exemplar Class 12 Biology solutions chapter 3 is fun and interesting for all those students who wish to learn about the different parts and how it works. This chapter is helpful for the students who wish to make a career in biology.

NCERT Exemplar Class 12 Solutions Subject Wise:

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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!

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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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A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg

 

An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)

K/2\,

Option 2)

\; K\;

Option 3)

zero\;

Option 4)

K/4

In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

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

Option 4)

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

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)

0.02

Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

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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