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4151.

The escape speed of a projectile on the earth's surface is 11.2 km s^(-1). A body is projected out with thrice this speed. What is the speed of the body far away from the earth? Ignore the presence of the sun and other planets.

Answer»

Solution :`V_e=11.2 kms^(-1)`, velocity of projection `=v=3v_e` Let m be the mass of projectile and `v_(0)` the velocity after it escape gravitational pull.
By LAW of CONSERVATION of ENERGY
`=(1)/(2)mv_(0)^(2)= (1)/(2)mv^(2)- (1)/(2)mv_(e )^(2)`
`v_(0)""=sqrt(v^2-v_(e )^(2))= sqrt(9v_(e )^(2)-v_(e )^(2))= sqrt(gv_(e )^(2))`
`=22.4sqrt(2)`
`=31.68 kms^(-1)`.
Discussion
4152.

Another name of absolute temperature is ___________.

Answer»

SOLUTION :THERMODYNAMIC TEMPERATURE
Discussion
4153.

The path of the light is called as __________.

Answer»

SOLUTION :RAY of LIGHT
Discussion
4154.

Human eye has a light sensitive screen on which images are formed. What is this screen called ?

Answer»

SOLUTION :This SCREEN is CALLED RETINA.
Discussion
4155.

Two caricatures presenting the situations of the year 1998 and 2017 obout playing on playground are given below. Observe those circatures. Express your opinion about arising of such different situations

Answer»

SOLUTION :1. In the first caricature, the scene of year 1998 SHOWS Mother forcefully bringing the child in the house for studying from PLAY and in second caricature of the year 2017, Mother is forcefully SENDING the child to play on the ground.

2. This situation has aroused due to the excessive use of modern technology.
3. In the year 1998, children got more time to play as there were no other distractions.
4. But now due to mobile phones and INTERNET, children are engrossed in playing games, watching movies and cartoons on TV or tablet or surfing through internet.
Discussion
4156.

An object of height 4 cm is placedin front of a concave lens of focal length 40 cm. If the objectdistance is 60 cm, find the position and height of the image.

Answer»

Solution :` (i) 1/f = 1/v -1/u"" therefore 1/u = 1/f + 1/u`
` therefore 1/u = 1/( - 40 cm) + 1/( - 60 cm) = - (1/( 40 cm) + 1/( 60 cm) )`
` = - ((3+2)/(120 cm) ) = - 5/120 cm`
` v - (120 cm)/5 = - 24 cm `
The image is FORMED at 24 cm from the lens. It is on the same side as the object.
(II) ` h_(2)/h_(1) =u/v"" therefore h_(2) = v/u h_(1)`
` thereforeh_(2) = ((-24 cm)/(- 60 cm)) xx 4 cm = 0.4 xx 4 cm = 1.6 cm`
The height of the image is 1.6 cm
Discussion
4157.

A body of mass 5 kg is taken to the centre of the earth. What will be its Weight there.

Answer»

SOLUTION :WEIGHT at CENTRE of EARTH will be 0 because g=0.
Discussion
4158.

Explain the sign Convention of lenses.

Answer»

SOLUTION :CARTESIAN SIGN conventions are used for measuring the various distance in the ray diagrams of spherical lenses.
According to Cartesian sign convention,
(i) The object is always placed on the left side of the lens.
(ii) All the distances are measured from the optical centre of the lens.
(iii) The distance measured in the same direction as that of INCIDENT light are taken as positive.
(iv) The distances measured against the direction of incident light are taken as negative.
(v) The distances measured upwards and PERPENDICULAR to principal axis is taken as positive.
(vi) The distances measured downwards and perpendicular to the principal axis is taken as negative.
Discussion
4159.

Attempts at various levels are performed for conserving environment. Role of the person is defined as per these levels. Some roles are given. Which role would you like to perform ?Why?

Answer»

SOLUTION :Students are EXPECTED to choose the role they WISH to perform for conserving ENVIRONMENT and explain why they PICKED up this role .
Discussion
4160.

Light enters from air into glass plate which has refractive indeed 1.5. Calculate the speed of light in glass (velocity of light in air is 3xx10^(8) m/s)

Answer»

Solution :`v_(g)=c/(a PROP g)`
`=(3XX10^(8))/1.5`
`=2XX10^(8)` m/sec
Discussion
4161.

Three block of masses m_1, m_2 & M_3 are connected by mass less stings as shown on a frictionless table. They are pulled with a force T_(3)=40N," If "m_(1)=10kg, m_(2)=6kg & m_(3)=4kg, then tension T_(2) will be

Answer»

20N
40N
10
32N

Solution :NET acceleration `=(T_(3))/(m_(1)+m_(2)+m_(3))=40/20=2m//s^(2)`
`T_(2)=(m_(1)+m_(2))a=16 XX 2=32N`
Discussion
4162.

State the Ohm.s law. Explain how it is used to define the SI unit of resistance.

Answer»

Solution :If I is the current flowing through a conductor and V is the potential difference (or voltage) across its ENDS, then according to Ohm.s law,
I `prop` V (at constant temperature).
This can also be written as,
`V prop I`
`:.` V = (constant) I
`{:( :. V/I = "constant"),( ""= R),( :. V = IR):}}`... ...(12.4)
In equation (12.4), R is constant for the given metallic wire at a given temperature and is called its resistance.
Resistance is the property of a conductor to oppose the flow of CHARGES through it.
The SI unit of resistance is ohm. It is represented by the GREEK letter `Omega` (Omega).
According to Ohm.s law,
`R = V/t`...... (12.5)
Definition of the SI unit of resistance : If the potential difference across the two ends of a conductor is IV and the current through it is 1 A, then the resistance R of the conductor is `1 Omega`.
`i.e., 1" ohm" = (1 "volt")/(1 " AMPERE") (1 Omega = 1V//1A)`
Discussion
4163.

During inelastic collision between two bodies, which of the following quantities always remain conserved ?

Answer»

TOTAL KINETIC energy
Total MECHANICAL energy
Total LINEAR momentum
Speed of each body

Answer :C
Discussion
4164.

Name the colours that constitute white light in the order of increasing angle of deviation.

Answer»

SOLUTION :Red, Orange, YELLOW, Green, BLUE, Indigo, and Violet.
Discussion
4165.

Balance the following reaction ""_6C^(14) to ""_(-1)e^(0)+ ?

Answer»

SOLUTION :`""_(6)C^(14) to ""_(-1)e^(0) + ""_(7)N^(14)`
Discussion
4166.

Tube feet , Setae , Parapodia , Sucker

Answer»

SOLUTION :Tube FEET . (Tube feet are LOCOMOTORY organs of Echinoderms, the REMAINING are locomotory of ANNELIDS. )
Discussion
4167.

What are collisions ? Explain the possible types of collision ? Develop the theory of one dimensional elastic collision .

Answer»

Solution :A Process in which the motion of a system of particles changes but keeping the total momentum conserved is called collision .
Collisions are two types : (1) ELASTIC (2) inelastic .
To show relative velocity of approach before collision is EQUAL to relative velocity of separation after collision
Let two bodies of masses`m_(1) ,m_(2)` are moving with velocities`u_(1) ,u_(2)` along the same LINE in same direction collied elastically .
Let their velocities after collision are `v_(1) and v_(2)` .

According to the LAW of conservation of linear momentum
According to the law of conservation of linear momentum
`m_(1)u_(1)+m_(2)u_(2)=m_(1)v_(1)+m_(2)v_(2)`
or`m_(1)(u_(1)-v_(1))=m_(2)(v_(2)-u_(2)) "" ...(1)`
According to the law of conservation of kinetic energy
`(1)/(2)m_(1)u_(1)^(2)+(1)/(2)m_(2)u_(2)^(2)=(1)/(2)m_(1)v_(1)^(2)+(1)/(2)m_(2)v_(2)^(2)`
`m_(1)(u_(1)^(2)-v_(1)^(2))=m_(2)(v_(1)^(2)-u_(1)^(2))""...(2)`
Dividing eqn . (2) by (1)
`(u_(1)^(2)-v_(1)^(2))/(u_(1)-v_(1))=(v_(2)^(2)-u_(2)^(2))/(v_(2)-u_(2))or`
` u_(1)+v_(1)=u_(2)+v_(2)rArru_(1)-u_(2)=v_(2)-v_(1) "" ...(3)`
i.e , In elastic collisions relative velocity of approach of the two bodies before collision = relative velocity of separation of the two bodies collision .
Velocities of two bodies after elastic collision :
To Find `v_(1), " put "v_(2)=u_(1)-u_(2)+v_(1)" in eqn".(1)`
`m_(1)u_(1)+m_(2)u_(2)=m_(1)v_(1)+m_(2)(u_(1)-u_(2)+v_(1))`
`m_(1)u_(1)+m_(2)u_(2)=m_(1)v_(1)+m_(2)u_(1)-m_(2)u_(2)+m_(2)v_(1)`
`m_(1)u_(1)+m_(2)u_(2)-m_(2)u_(1)+m_(2)u_(2)=v_(1)(m_(1)+m_(2))`
`u_(1)(m_(1)-m_(2))+2m_(2)u_(2)=v_(1)(m_(1)+m_(2))`
`thereforev_(1)=(m_(1)-m_(2))/(m_(1)+m_(2))" "u_(1)+(2m_(2))/(m_(1)+m_(2))" " u_(2)""....(4) `
Similarly , `v_(2)=(u_(2)(m_(1)-m_(2)))/(m_(1)+m_(2))+(2m_(2)u_(1))/(m_(1)+m_(2))"" ...(5) `
Discussion
4168.

Species

Answer»

SOLUTION :The group of organisms that can produce fertile INDIVIDUALS through NATURAL REPRODUCTION is CALLED a species.
Discussion
4169.

How many images do we see between two parallel mirrors ?

Answer»

SOLUTION :INFINITE.
Discussion
4170.

The elements in periods 2 and 3 having stable electronic configuration .

Answer»

SOLUTION :(i) NEON(II) ARGON
Discussion
4171.

What is short-circuiting of an electric circuit ? An electric motor of 1.5 kW power rating is operated in a domestic electric circuit of current rating 5A. What would happen when it is switched ON ? Give reason for your answer.

Answer»

Solution :Situation when live wire and NEUTRAL wire come into direct contact, CURRENT in the circuit ABRUPTLY increases.
P = 1.5 `xx `1000 W = 1500 w
p = VI or I= `(p)/(v) = (1500 W)/(220 V) = 6.8`
Electric current required (6.8 A) is more than the current rating of the circuit, i.e., 5A. Hence the fuse will melt and the electric MOTOR will stop working.
Discussion
4172.

A convex lens forms a virtual image of an object placed…….. .

Answer»

at infinity
at `2F_(1)`
at`F_(1)`
between`F_(1)` and opitcal CENTRE O

Answer :between `F_(1)` and OPTICAL centre O
Discussion
4173.

Who discovered the magneticeffect of an electriccurrent ?

Answer»

FARADAY
OERSTED
VOLTA
AMPERE

SOLUTION :Oersted
Discussion
4174.

(a) What is aqueous homour ? (b) What is vitreous humour ?

Answer»

Solution :(a) Aqueous humour is a transparent viscous LIQUID in the space between cornea and eye LENS.
(B) Vitreous humour is a transparent jelly in the space between eye lens and RETINA.
Discussion
4175.

If in the circuit, the resistor is replaced by a motor, in which form will the energy given by the cell get transformed into?

Answer»

SOLUTION :The energy from the cell will GET transformed from ELECTRICAL energy into MECHANICAL energy by the cell.
Discussion
4176.

Calculate the kinetic energy of a body of mass 0.1 kg and momentum 20 kg ms^(-1)

Answer»

SOLUTION :Given :P20 kg `MS^(-1),m=0.1 kg `
Kinetic energy `K=(1)/(2)mv^(2)` and
Momentum `p=mv` or `v=(p)/(m)`
Eliminating v,
`K=(1)/(2)mxx((p)/(m))^(2)=(p^(2))/(2m)`
`therefore K=((20)^(2))/(2xx0.1)=2000 J=2xx10^(3)J`
Discussion
4177.

Where is the image formed in an eye ?

Answer»


ANSWER :RETINA
Discussion
4178.

Fill in the blanks: (i) The amount of work done to move charge from one point to another is called_____. (ii) When a circuit is open,_____ cannot pass through it.

Answer»


ANSWER :CURRENT
Discussion
4179.

Vertebrates have been slowly originated from invertebrates .

Answer»

Solution :(1) When the carbon dating method was used to assess the age of fossils, it wasunderstood that invertebrates were PRESENT on THEEARTH much before the vertebrates. (2) The fossile of invertebrates arepresent in lower layers of earth's strata. They were seen in Palaeozoic era of geological time period. (3) Vertebrates dominated during Coenozoic era. Their fossils are seen in the UPPER strata of the earth's CRUST. (4) The structural complexity also increased in vertebrates. All these facts indicate thatvertebrates have been slowly originated from invertebrates.
Discussion
4180.

Achal 's teacher is teaching their class about fuels today. She tells them 'Always turn off the engine of your car at red lights'. The next day Achal's father drives him to school. At the red light he does not turn the engine off. When Achal asks him to do so he says that the light is of short duration and this won't save the fuel. Based on the above statement, answer the following questions. (i) Which type of fuel is used in vehicles? Is it renewable or non-renewable? (ii) How can you contribute towards saving these fuels at your level? (iii) What values are being neglected by Achal's father?

Answer»

SOLUTION :(i) Fossil fuel - non-renewable.
(ii) (a) Travelling in public transport, arranging for car pools.
(b) OPTING for CNG as a motor fuel instead of petrol and diesel.
(iii) CONCERN for ENVIRONMENT, judicious use of non-renewable SOURCES of energy.
Discussion
4181.

Two devices of ratings 44W, 200V and 11W, 220V are connected in series. The combination is connected across a 440V mains. The fuse of which of the two devices is likely to burn when switch is on ? Justify your ,answer.

Answer»

Solution :The fuse of device of ra.ting 11W, 220 V will burn.
`R=(V^(2))/(W) :.` RESISTANCE of 11 W device will be FOUR times than that of the device of 44W.
`:.` Voltage across 11 W= 352 V
`:.` Volatge across 44W= 88 V
352 V across the device of 11W, 220V rating is sufficient to BUM the fuse of the device.
Discussion
4182.

A light incident on a plane mirror subtends an angle of 60^(@) from the surface of mirror. The angle of reflection is __________________.

Answer»


SOLUTION :As the incident ray subtends an ANGLE of `60^(@)` from the mirror SURFACE, the angle of incidence `angle i = 30^(@)` and HENCE `angle R = 30^(@)`
Discussion
4183.

What do you infer form this?

Answer»

Solution :Sound is a form of energy which can TRAVEL in the form of WAVES through the MEDIUM.
Discussion
4184.

Refractive index of water is 4/3. calculate the speed of light in water. Speed of light in vacuum is 3xx10^(8)ms^(-1).

Answer»

Solution :Refractive index of WATER=`("speed of light in VACUUM")/("speed of light in water")`
`therefore (4)/(3)=(3XX10^(8))/("Speed of light in water")`
or Speed of light in water`=(3)/(4)XX(3xx10^(8))`
`=2*25xx10^(8)ms^(-1)`
Discussion
4185.

What is the function of an earth wire? Why is it necessary to earth the metallic appliances?

Answer»

Solution :Sometimes, the insulation of LIVE wire is torn and due to this the live wire touches the metallic body of the appliances. This CAUSES the flow of current in metallic body. This current flows to the Earth through the earth wire and does not HARM the user of the appliances.
Therefore to prevent the user getting an ELECTRIC shock, due to leakage of current to metallic body, Earth wire MUST always be used.
Discussion
4186.

_________are green coloured plastids.

Answer»

Chloroplast
Chromoplast
Leucoplast
Stele

Answer :a
Discussion
4187.

If the gap between steel sails on railway track of 66m long is 3.63 cm at 10^(@)C. Then at what value of temperature will be just touch of steel is 11xx10^(-6)""^(@)C

Answer»

SOLUTION :`L_(0)=66 m`
`L_(o)=6600 cm`
`alpha=11xx10^(-6)""^(@)C`
`alpha=(DeltaL)/(L_(o) DeltaT)`
`L_(t)-L_(o)=3.63 cm`
`DeltaL=3.63 cm`
`t_(1)=10^(@)C t_(2) =?`
so `DeltaT=(DeltaL)/(L_(o)xxalpha)`
`DeltaT=(3.63)/(6600xx11xx10^(-6))`
`t_(2)-t_(1)=50`
`t_(2)=10=50`
so final temperature `t_(2)=50+10=60^(@)C`
Discussion
4188.

If the scalar and vector products of two vectors vecA and vecB are equal in magnitude, then the angle between the two vectors is

Answer»

`45^(@)`
`90^(@)`
`180^(@)`
`120^(@)`

Solution :`|VECA*vecB|=|vecA xx vecB|`
`AB cos THETA=AB SINTHETA`
`1=tan theta`
`tan theta=1`
`tan theta = tan45^(@)`
`theta=45^(@)`
Discussion
4189.

How does the resistance of a wire depend on its radius?

Answer»

SOLUTION :The resistance of a wire is inversely PROPORTIONAL to the SQUARE of its RADIUS.
Discussion
4190.

Solar energy can be used in

Answer»

SOLAR cooker
Photosynthesis
Solar cell
All of these

Answer :A::B::C::D
Discussion
4191.

What is meant by reflection of light ?

Answer»

Solution :The PROCESS through which LIGHT rays FALLING on the SURFACE on an object are sent back is called as REFLECTION of light.
Discussion
4192.

Mention the anglebetween a current - carrying straightconductorand magnetic field for whichthe force experienced by the conductorplaced in a magnetic fieldis maximum .

Answer»

SOLUTION :`90^(@)`
Discussion
4193.

Name the instrument used to measure electric potential difference.

Answer»

Solution :The ELECTRIC potential DIFFERENCE is measured with the instrument/device CALLED VOLTMETER.
[Note: It is a high-resistance instrument which is ALWAYS connected in parallel to the conductor across which the potential difference is to be measured.]
Discussion
4194.

Discuss the role of magnesium in plants.

Answer»

RESPIRATION
Excretion
Transpiration
NONE of the above

Answer :C
Discussion
4195.

Effective disaster management makes us well pepared for future. Explain.

Answer»

Solution :i. Any type of disaster whether minor or major, short- term or long-term, needs to be overcome and hence effective disaster MANAGEMENT is of importance.
ii. Disaster management involves either prevention of disaster or MAKING required arrangements to face it or at least achieveing the abilities to face it.
iii. Disaster management includes the use of scientific methods to obtain data and its careful observation and analysis for achieveing and improging the capability to face the disaster.
IV. Base on this analysis, attempts can be made to minimize the losses.
V. The data also helps to prepare action plans for future disasters by STUDYING various aspects of disaster such as preventive measures, rehabilitation and reconstruction and the method of effective execution of the plan.
Thus, effective disaster management makes us well prepared for future.
Discussion
4196.

The formula for electric current is ………. .

Answer»

`I = QT`
`I = Q/t`
`I = t/Q`
`I =W.t`

SOLUTION :`I = Q/t`
Discussion
4197.

The amountof force requiredto produce an acceleration of1 ms^(-2) in a body of mass 1 kg called ____________.

Answer»

SOLUTION :UNIT FORCE
Discussion
4198.

(genetically, recombination, gamete, crossing over, haploid, diploid, Meiosis-II, meiosis-I, zygote) ……………………… is just like mitosis. In this stage, the two haploid daughter cells formed in ……………………… undergo division by separation of recombined sister chromatids and four .......................... daughter cells are formed. Process of ......................... production and spore formation occurs by meiosis. In this type of cell division, four haploid (n) daughter cells are formed from one ......................... cell. During this cell division, .............................. occurs between the homologous chromosomes and thereby genetic ........................ occurs. Due to this, all the four daughter cells are ..................... different from parent cell and from each other too.

Answer»

Solution :Meiosis-II is just like mitosis. In this stage, the two haploid daughter cells FORMED in meiosis-I UNDERGO division by separation of recombined sister chromatids and four haploid daughter cells are formed. Process of gamete production and spore formation occurs by meiosis. In this type of cell division, four haploid (n) daughter cells are formed from one diploid cell. During this cell division, crossing over occurs between the homologous CHROMOSOMES and thereby genetic RECOMBINATION occurs. Due to this, all the four daughter cells are genetically different from parent cell and from each other too.
Discussion
4199.

What is the law, (V)/(I)= constant For a conductor ?

Answer»

SOLUTION :OHM's LAW
Discussion
4200.

Students were asked to observe the permanent slides showing different stage of budding in yeastunder high power of a microscope. (a) Which adjustment scraw (coarse/fine) were you asked to move to foucs the slides? (b) Draw three diagrams in correct sequence showing budding in yeast.

Answer»

SOLUTION :(a) A fine adustment scraw is MOVED to FOCUS the slides.
(B)
Discussion