Homework Help > CBSE Class 09
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My doubt is to the institution/dignitaries of myCBSEguide. I am a student studying in class 9. I am too much worried about the consumption of time I take for attending 1,2,3,4, and 5 marks questions . Usually I takes 1/2 sheets for attending 3,4 and 5 marks questions. My teachers advices me I am writing too much than the limit. But,unfortunately I could't control my writing. By doing so I miss so many questions which I know. The board exams are nearer to me. So, respected dignitaries please send me how to manage time and how much to write in my exams.

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The curved surface area of cone is 550cm²and the height of cone is 24cm. Find volume.

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Let Radius of Cone is r and slant height is l.
height of Cone (h) = 24 cm
CSA of cone = 550 cm^{2}
We know,
$l=\sqrt{{r}^{2}+{h}^{2}}$
=> $l=\sqrt{{r}^{2}+576}............\left(1\right)$
Also,
$CSA=\pi \times r\times l$
=> $550=\frac{22}{7}\times r\times \sqrt{{r}^{2}+\hspace{0.17em}576}$
Squaring both side,
=> $302500=\frac{484{r}^{2}({r}^{2}+576)}{49}$
=> $30625={r}^{4}+576{r}^{2}$
=> ${r}^{4}+576{r}^{2}30625=0$
Put ${r}^{2}=t$
=> ${t}^{2}+576t30625=0$
=> ${t}^{2}+625t49t30625=0$
=> $t(t+625)49(t+625)=0$
=> $(t+625)(t49)=0$
=> $t+625=0ort49=0$
=> t =  625 0r t = 49
=> r^{2 } = 625 is not possible so r^{2} = 49
=> r = 7
put in (1), we get
$l=\sqrt{49+576}\phantom{\rule{0ex}{0ex}}$
=> $l=\sqrt{625}\phantom{\rule{0ex}{0ex}}$
=> l = 25
=>$VolumeofCone=\frac{1}{3}\pi {r}^{2}h$
=> $VolumeofCone=\frac{1\times 22\times 49\times 24}{3\times 7}\phantom{\rule{0ex}{0ex}}$
=> Volume = 1232cm^{3}
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What is disease and define it's types

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In Simple words disease is as name word itself suggests without ease.
Disease is an abnormal condition of a part, organ, or system of an organism resulting from various causes, such as infection, inflammation, environmental factors, or genetic defect, and characterized by an identifiable group of signs, symptoms, or both.
<font face="Arial">Types of Diseases</font>
<font face="Arial">•</font> <font face="Arial">Acute diseases</font>
<font face="Arial"></font> <font face="Arial">The symptoms appear suddenly.</font>
<font face="Arial"></font> <font face="Arial">These diseases are short term ie the symptoms last for short period of time.</font>
<font face="Arial"></font> <font face="Arial">Eg. Influenza (Flu) , Common cold.</font>
<font face="Arial">• Chronic diseases</font>
<font face="Arial"></font> <font face="Arial">These diseases long term diseases.</font>
<font face="Arial"></font> <font face="Arial">Their symptoms develop gradually and are long lasting.</font>
<font face="Arial"></font> <font face="Arial">Eg. TB, Cancer etc</font>
<font face="Arial">• Congenital diseases</font>
<font face="Arial"></font> <font face="Arial">These are inborn diseases i.e. present from birth.</font>
<font face="Arial"></font> <font face="Arial">Most of the diseases are permanent and generally not easily curable.</font>
<font face="Arial"></font> <font face="Arial">They could be due to genetic abnormality or metabolic disorder.</font>
<font face="Arial"></font> <font face="Arial">Eg. Down syndrome, Hemophilia, colour blindness, Sickle cell anaemia etc</font>
<font face="Arial">• Acquired diseases</font>
<font face="Arial"></font> <font face="Arial">The diseases which a person gets in his or her life time (i.e. after birth) are called acquired diseases.</font>
<font face="Arial"></font> <font face="Arial">Acquired diseases are classified in to two categories</font>
<font face="Arial">1)</font> <font face="Arial">Communicable diseases (Infectious diseases)</font>
<font face="Arial">2)</font> <font face="Arial">Noncommunicable diseases (Noninfectious diseases)</font>
<font face="Arial">1) Communicable Diseases</font>
<font face="Arial">•</font> <font face="Arial">Communicable diseases are caused by pathogens such as virus, bacteria, protozoan, worms or fungi.</font>
<font face="Arial">•</font> <font face="Arial">The organism causing the disease may be transmitted from an infected person to another by means of air, water, food, physical contact or insects (vectors).</font>
<font face="Arial">•</font> <font face="Arial">Communicable diseases can be further classified on the basis of the causative agents like Bacterial diseases, Viral diseases, Helminth diseases, Fungal diseases etc.</font>
<font face="Arial">2) NonCommunicable Diseases</font>
<font face="Arial">•</font> <font face="Arial">These are non infectious diseases ie do not spread from an infected person to other healthy person</font>
<font face="Arial">•</font> <font face="Arial">These diseases include deficiency diseases, degenerative diseases, cancer etc.</font>
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The probability of guessing the correct answer to a certain question is x/2 (x upon 2). If the probability of not guessing the correct answer to the question is 2/3 ( 2 upon 3) , then find x.

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Ans. Let A denote the probability of guessing correct answer and B denote the probability of not guessing correct answer.
Then, $p\left(A\right)=\frac{x}{2}andp\left(B\right)=\frac{2}{3}$
$p\left(A\right)+\hspace{0.17em}p\left(B\right)=1$
=> $\frac{x}{2}+\frac{2}{3}=1$
=> $\frac{x}{2}=1\frac{2}{3}$
=> $\frac{x}{2}=\frac{1}{3}$
=> $x=\frac{2}{3}$
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Bhor's atomic model

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In 1913 Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus. The motion of the electrons in the Rutherford model was unstable because, according to classical mechanics and electromagnetic theory, any charged particle moving on a curved path emits electromagnetic radiation; thus, the electrons would lose energy and spiral into the nucleus. To remedy the stability problem, Bohr modified the Rutherford model by requiring that the electrons move in orbits of fixed size and energy. The energy of an electron depends on the size of the orbit and is lower for smaller orbits. Radiation can occur only when the electron jumps from one orbit to another. The atom will be completely stable in the state with the smallest orbit, since there is no orbit of lower energy into which the electron can jump.
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How can we define sound?

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Sound is a vibration that propagates as a typically audible mechanical wave of pressure and displacement, through a transmission medium such as air or water.
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Vibrations that travel through the air or another medium and can be heard when they reach a person's or animal's ear.
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What is molar mass

Molar mass is the amount of mass in one mole of a substance. A mole is used in chemistry as a counting unit indicating the amount of ions, atoms, molecules or formula units in a specific chemical sampl
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The mass of one mole of the substance is called molar mass of that substance. Its units are g/mol. If the substance is atomic, its molar mass is equal to gram atomic mass. If the substance is molecular, its molar mass is equal to gram molecular mass.
Molar mass of magnesium (Mg)= 24g/mol
Molar mass of oxygen (O_{2})= 2x16= 32g/mol
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Name the three organs of the government

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The three main organs of the government includes executive branch,legislature branch and the judiciary branch.
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Three main organs of Government
1) Legislature 2) Executive 3) Judiciary
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There are how many members in Look shaba

It is Lok shaba
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There are 545 members in 16th Lok Sabha. 543 are elected and 2 are nominated.
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543
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what is circumcentre

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Circumcentre is the point of intersection of three perpendicular bisectors
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Why judiciary enjoys high level of confidence among the people?

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Judiciary is the most powerful weapon of the constitution of a country. The supreme court and the high court have the power to interpret any law of legislature or any action of executive. Judiciary stops the misuse of the governments power in making and with reference to PIL if any person is hurt by any law or action can file a PIL in the court against it.
Some reasons because of judiciary enjoy highest level of confidence among the public.
1) Judiciary is independent and powerful in democracies. All the courts at different levels in a country put together is called Judiciary.
2) The Supreme Court controls the judicial administration in the country. The powers and the independence of Indian Judiciary allow it to act as guardian of Fundamental Rights
3) Citizens have the right to approach the courts to seek remedy in case of any violation of their rights.
4) The courts also intervene to prevent the misuse of government’s power to make decisions.
5) In the recent years, courts have given several judgments and directives to protect public interests and human rightsThanks (2)
A stone of mass 4gm is to be thrown into a well. The sound is to be heard after 4sec .find the depth of well if (g=10m/s^{2})and speed of sound is 340m/s.

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For the 1st part the stone is falling under gravity. Let t_{1} be the time from release to splashdown.
d =depth
So d= gt_{1}^{2}/2  (1)
After splashdown the sound travels back up. Using 330m/s for the speed of sound this gives:
d=330×t_{2} (2)
We also know that:
t_{1}+t_{2}=4s (3)
Combining (1)and(2) we get:
330t_{2}= gt_{1}^{2}/2
From (3)⇒
t_{2}=(4−t_{1})
So:
330(4−t_{1})=gt_{1}^{2}/2
5t_{1}^{2}+330t1320=0
t_{1}^{2}+66t264=0
Solving this quadratic equation using Discriminant formula and ignoring the ve root we get
t_{1}=3.78s
So t2=4−3.78=0.22s
So d=330×t_{2}=330×0.22=72.6m
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this is $\frac{19h}{85}insteadof\frac{19h}{5}$
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Ans. Let Depth of Well = h
${t}_{stone}+{t}_{sound}=4..................\left(1\right)\phantom{\rule{0ex}{0ex}}$
$For{t}_{stone}(freefallingbody):\phantom{\rule{0ex}{0ex}}$
$h=\frac{1}{2}g{t}^{2}\phantom{\rule{0ex}{0ex}}=t=\sqrt{\frac{2h}{g}}$
${t}_{stone}=\sqrt{\frac{2h}{10}}\phantom{\rule{0ex}{0ex}}$
= > ${t}_{stone}=\sqrt{\frac{h}{5}}\phantom{\rule{0ex}{0ex}}$
$For{t}_{sound}(uniformmotion):\phantom{\rule{0ex}{0ex}}$
$h=ut\phantom{\rule{0ex}{0ex}}=t=\frac{h}{u}$
${t}_{sound}=\frac{h}{340}$
Put Both values values in eq (1), We get
$\sqrt{\frac{h}{5}}+\frac{h}{340}=4$
=> $\sqrt{\frac{h}{5}}=4\frac{h}{340}$
Squaring both sides
$\frac{h}{5}=16+\frac{{h}^{2}}{{340}^{2}}\frac{2h}{85}$
=> $\frac{{h}^{2}}{115600}+16=\frac{h}{5}+\frac{2h}{85}$
=> $\frac{{h}^{2}}{115600}\frac{19h}{5}+16=0$
Solve for h and you ll have answer
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what do you understand by text orientation

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It essentially is the means of how you want to view your text messages.
This can be horizontally or vertically displayed on the screen of your Computer.Thanks (0)
A rectangular tank measuring 5m * 4.5m * 2.1m is dug in the centre of the field measuring 13.5m * 2.5m. The earth dug out is spread evenly over the remaining portion of the field. How much is the level of the field raised?

How can you dug a tank of width 4.5 m in field of width 2.5 m ?
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Area of field=13:5×2:5=33:75
Upper area of tank=5×4:5=22:5
Area of field on which soil is spread=33:75_22:5
=11:25m Volume of tank=5×4:5×2:1=47:25m^3
Raised in level=volume of tank/area of field on which
soil spread=47:25/11:25=4:2
So,raised level=4:2m
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Can you tell me the solutions of OTBA material hindi 2016

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http://mycbseguide.com/downloads/cbseclass09hindicoursea/1904/cbseotbamaterial/12/ you can downoad it from here
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Find the energy in kilowatt hours consumed by a machine of power 500watts?

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We know 1 Kw = 1000W
Power of machine in Kw: 500/1000 = 1/2 Kw
Power consumption in 1 hour = 1/2 * 1 = 1/2Kwh
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0.18 grams of glucose contains how many atoms

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So, glucose's molecular formula is C_{6}H_{12}O_{6}, which means that every molecule of glucose contains Six carbon atoms ,Twelve hydrogen atoms, Six oxygen atoms.
Molar mass of C = 12 g mol^{1}
Molar mass of H = 1 g mol^{1}
Molar mass of O = 12 g mol^{1}
There fore,
Molar mass of C_{6}H_{12}O_{6}=(6x12) + (12x1) + (6x16) = 72 + 12 + 96 = 180 g mol^{1}
Now we can calculate the number of moles of glucose as follows:
The number of moles of glucoses n = w/M , where w is weight in gram and M is molar mass.
=> 0.18/180 = 10^{3 }moles
It is also possible to get the number of atoms in the given sample by multiplying the number of moles with Avogadro number, N_{A}
Thus
the number of atoms = n.N_{A, }Where N_{A} = 6.022 x 10^{23}
In above glucose sample,
the no. of glucose atomes = 10^{3} x 6.022 x 10^{23} = 6.022 x 10^{20 }
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0.025 moles of methane contain how much grams

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Gram atomic mass of methane=CH4=12+4×1
=16 no of moles=given mass÷gram atomic mass
0:025=given mass÷16
So,given mass=16×0:025
Given mass=0:4 gram
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How far it is correct to say that both pressure and winds
conditions over india are unique. What Information would you use to support your answer?

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If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.

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Ans.
Molar mass of a substance is a mass of 6.023 X10^{23} molecules.
Molar mass of Oxygen molecule i.e N is 2 X 8 = 16 g.
Thus 6.023 X 10^{23} molecules weigh = 16 g
1 molecule of Oxygen weighs = 16/6.02 X 10^{23} = 2.66 X 10^{23} g
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Ans. The mass of 1 atom = Gram atomic mass of atom/ 6.022 × 10^{23}
So, the mass of 1 atom of oxygen = Gram atomic mass of oxygen atom/ 6.022 × 10^{23} = 16g/ 6.022 × 10^{23} =
2.66 × 10^{23} g
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If one mole of nitrogen molecules weighs 28 g, calculate the mass of one molecule of nitrogen in grams.

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Answer: The mass of 1 atom = Gram atomic mass of atom/ 6.022 × 10^{23}
So, the mass of 1 atom of nitrogen = Gram atomic mass of nitrogen atom/ 6.022 × 10^{23} = 28g/ 6.022 × 10^{23} =
4.65 × 10^{23} g
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Ans. Molar mass of a substance is a mass of 6.023 X10^{23} molecules.
Molar mass of nitrogen molecule i.e N is 2 X14 = 28 g.
Thus 6.023 X 10^{23} molecules weigh = 28 g
1 molecule of nitrogen weighs = 28/6.02 X 10^{23} = 4.65 X 10^{23} g
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In an experiment, 4.9g of copper oxide news obtained nfrom 3.92g of copper . In another experiment,4.55g of copper oxide gave, on reduction, 3.64 g of copper . Show that these figure verify the law of constant proportion

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Case I
Mass of copper= 3.92g
Mass of copper oxide= 4.9g
% of copper in oxide = (Mass of copper/Mass of copper oxide) x 100
= 80%
So, % of oxygen = 10080= 20%
Case II
Mass of copper= 3.64g
Mass of copper oxide= 4.55g
% of copper in oxide = (Mass of copper/Mass of copper oxide) x 100
= 80%
% of oxygen= 10080=20%
Thus,copper oxide prepared by any of the given methods contains copper and oxygen in the same proportion by mass.Hence, it proves the law of constant proportions.
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How to derive speed = wavelength * frequency

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As we know, speed= Distance travelled/Time taken
Suppose a wave travels a distance $\lambda $ which is its wavelength in time T,
v = $\lambda $ / T
Here T is the time taken by one wave. 1/T becomes the number of waves per second and is known as frequency of the wave.
Thus v = $\lambda $ x f
i.e. Speed = Wavelength x Frequency
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what is canal ray?

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Canal rays: These are also known as anode rays which are made up of positively charged material particles known as protons. They are called as canal/anode rays because they seems to be coming from a perforated anode used in a discharge tube experiment. The charge to the mass ratio (e/m ratio ) is not constant for these rays, and has been found different for different gases used in the discharge tube. The mass of proton has been found to be nearly equal to that of hydrogen atom.(nearly 1).
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An anode ray (also positive ray or canal ray) is a beam of positive ions that is created by certain types of gas discharge tubes. They were first observed in Crookes tubes during experiments by the German scientist Eugen Goldstein, in 1886.
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positively rays
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AOB is a right Triangle right angled at O=12.5 centimetre where C is the midpoint of AB that is AC =CB. AO =7 cm, find the area of triangle AOB.

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Can water boil at 0 degree celcius?

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Yes you can! Only if By any means you make the vapour pressure of water at the 'desired' temperature (0°C if you like) equal to (or greater) the atmospheric pressure of that place, your water will boil.
Aliter, reduce atmospheric pressure. Keep the water in vacuum.Thanks (0)
Explain the uses of sonar

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SONAR is an apparatus which is used to find the depth of a sea or to locate the underwater things like shoals of fish,shipwrecks, and enemy submarines. It works by sending short bursts of ultrasonic sound from a ship down into seawater and then picking up the echo produced by the reflection of ultrasonic sound from underwater objects. Thus, the time it takes for an echo to return is used to find out how far away something is.
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 Sound navigation and ranging
 It is used in detected sumarine , rocks , etc
 It receives the depth of the sea
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1. What are the rules to be followed while entering the following in OOo Calc?
a) numbers
b) text
c) formulas

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Suggest the calc functions that can be used for carrying out following operations :
1.to calculate total marks of a student if his marks in five subjects are given in five different cells.
2. To calculate average sales made by salesman of a company , if sales made by each of the salesman is available.
3. To find out the marks of top scorer in a class, if marks of all the students are available.
4. To find out minimum quoted rate from various quotations available.

Yaar koi jaldi answer batao..... mujhe home work karni hai....
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