CBSE > Class 09 > Science | CBSE Board | Homework Help

The persistence of sound in a big hall due to multiple reflection of sound is called reverberation. It can be reduced by using soft,sound absorbing materials like curtains,carpets,seat civers etc.

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Harsh Gadekar 7 years, 1 month ago

It can be reduced by covering the ceiling and walls of the enclosed space

2Thank You

Harsh Gadekar 7 years, 1 month ago

The repeated reflection that results in persistence of sound is called reverberation

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ANSWER

What is abiotic

Posted by Tanvi Rathore 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Jay Joshi 7 years, 1 month ago

All the non living things.

2Thank You

ANSWER

What is the molecular mass of ammonium sulphate

Posted by Ajay Kumar Singh 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Gaurav Seth 7 years, 1 month ago

Molecular mass of (NH4)2SO4 :
= (N2H8SO4)
=2* 14 +1 *8 +32+16*4
=28+8+32+64
=132

1Thank You

ANSWER

What is biotic components

Posted by Tanvi Rathore 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Jay Joshi 7 years, 1 month ago

All the living things

1Thank You

ANSWER

Differtent betwween chronic and acute

Posted by Rohit Kumar 7 years, 1 month ago

CBSE > Class 09 > Science

2 answers

Banasri Subhasmita 7 years, 1 month ago

Acute are diseases which last for a short period of time Chronic are diseases which last for a long period of time

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Tanvi Rathore 7 years, 1 month ago

Chronic are for long term and acute is for short term

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ANSWER

Explain, why prevention is better than cure?

Posted by Jyoti Verma 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Banasri Subhasmita 7 years, 1 month ago

Taking some precautions in life prevents us from acquiring diseases. It is tough to undergo symptoms of the disease. Diseases also take some time to be cured. So "Prevention is better than cure"

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ANSWER

How the diseases AIDS spread?

Posted by Jay Joshi 7 years, 1 month ago

CBSE > Class 09 > Science

2 answers

Mohit Talmale 7 years, 1 month ago

By breast feeding,sexual contact,the disease may cause to baby of the pregnent lady if she is suffering from AIDS,transmitting AIDS infectected blood,using used syringes

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Pushpendra Jha 7 years, 1 month ago

By sexual contact

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ANSWER

What is adipose tissue

Posted by Kuldeep Singh Cr7 7 years, 1 month ago

CBSE > Class 09 > Science

2 answers

Ritu Jha 7 years, 1 month ago

It fills empty space between organs

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Řaýn Ahmad 7 years, 1 month ago

Adipose tissue is fat storing tissue

4Thank You

ANSWER

List any two difference between pteridophytes and phanerogams

Posted by Srinivasan Pandurangan 7 years, 1 month ago

CBSE > Class 09 > Science

0 answers

ANSWER

What is ratio of forces between two masses. Kept at a certain distance in air to the force between them when kept in any other medium

Posted by Vishal S Shuklq 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Meghna Thapar 6 years, 1 month ago

Suppose two balls A and B, of masses m_A and m_B are travelling in the same direction along a straight line at different velocities u_A and u_B. And there are no other external unbalanced forces acting on them. Let u_A > u_B and the two balls collide with each other. During collision which lasts for a time t, the ball A exerts a force F_AB on ball B and the ball B exerts a force F_BA on ball A.

Suppose v_A and v_B are the velocities of the two balls A and B after the collision, respectively.

The momenta of ball A before and after the collision are m_A u_A and m_A v_A. The rate of change of its momentum (or F_AB, action) during the collision will be

m_A (v_A - u_A)/t

Similarly, the rate of change of momentum of ball B (= F_BA or reaction) during the collision will be

m_B (v_B - u_B)/t.

According to the third law of motion, the force F_AB exerted by ball A on ball B (action) and the force F_BA exerted by the ball B on ball A (reaction) must be equal and opposite to each other. Therefore,

F_AB = – F_BA

m_A (v_A - u_A)/t = -m_B (v_B - u_B)/t. This gives,

m_A u_A + m_B u_B = m_A u_A + m_B v_B

where m_A and m_B are masses of the bodies, u₁ and u₂ are initial velocities of the bodies and v₁ and v₂ are final velocities of the bodies.

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ANSWER

A cyclist is riding on a circular path of radius 5 m with a speed of 10 m/s.what is the change in velocity when he has travelled through a semicircle

Posted by Vrunda Kotecha 7 years, 1 month ago

CBSE > Class 09 > Science

0 answers

ANSWER

Differentiate between saprophytes and phanerogams

Posted by Fatima Khatuda 7 years, 1 month ago

CBSE > Class 09 > Science

3 answers

Tanvi Sharma 7 years, 1 month ago

Sorry by mistake i write whivh its a which

0Thank You

Tanvi Sharma 7 years, 1 month ago

Saprophytes are the organisms that depend on dead and decaying organic. matter for nutrition ,The spermatophytes also known as phanerogams these are seed bearing plants • vascular tissues are present whivh forms a vascular system and they contain gymnosperm and angiosperms

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Fatima Khatuda 7 years, 1 month ago

I dont know

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ANSWER

What is ozone ? How does it affect the ecosystem

Posted by Sanjay05 Sanjay05 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Dude ? 7 years, 1 month ago

Ozone is a protective layer from ultraviolet rays...above atmosphere..it absorbs harmful uv rays from sun.it effects our enviroment by increasing earth's temperature which leads to produce green gases and global warming..increase of carbon dioxide in atmosphere

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ANSWER

What is natural selection?

Posted by V K 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Yogita Ingle 7 years, 1 month ago

Natural selection is the process by which individuals with characteristics that are advantageous for reproduction in a specific environment leave more offspring in the next generation, thereby increasing the proportion of their genes in the population gene pool over time. Natural selection is the principal mechanism of evolutionary change, and is the most important idea in all biology. Natural selection, the unifying concept of life, was first proposed by Charles Darwin, and represents his single greatest contribution to science.

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ANSWER

What is the best wat to remember formula of physics

Posted by Khushi Ojha 7 years, 1 month ago

CBSE > Class 09 > Science

2 answers

Adarsh Kumar 7 years, 1 month ago

You can also remember by the definition and statements.

2Thank You

Diya Agarwal 7 years, 1 month ago

Remember through the derivations

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ANSWER

Valency of an element X is 3. Write the the chemical formula of its oxide

Posted by Ritu Raj 7 years, 1 month ago

CBSE > Class 09 > Science

5 answers

Sayoni Debnath 7 years, 1 month ago

X2O3 . It is aluminium. So the formula will be Al2O3

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Adarsh Kumar 7 years, 1 month ago

Lithium oxide

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Garima Mittal 7 years, 1 month ago

X2O3

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Surya Datt Chaturvedi 7 years, 1 month ago

X2OH3

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Simran Gangwar 5 years, 11 months ago

2Thank You

ANSWER

What is difference between O2 ans 2O

Posted by Aishani Singh 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Akanksha Kumari? 7 years, 1 month ago

O2 represents one molecule of oxygen containing 2 atoms but 2O represents 2 separate atoms of oxygen .

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ANSWER

What is *** hormones

Posted by Monish Kumar 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Yogita Ingle 7 years, 1 month ago

The hormones involved in the development and control of the reproductive organs and secondary sexual characteristics are called *** hormones.The two common *** organs are Testosterone and estrogen.

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ANSWER

What are protozad diseases

Posted by Navya Chitturi 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Yogita Ingle 7 years, 1 month ago

Malaria : It is a disease caused by a protozoan called Plasmodium
Entamoeba histolytica causes Amoebiasis. It is a protozoan parasite that is present in the large intestine of a human.

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ANSWER

What is the relationship between Nm and m?

Posted by Akanksha Maurya 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Yogita Ingle 7 years, 1 month ago

Nanometre is a very, very small unit of measuring length. It is written as nm.
1 nanometre = 1/10⁹ metre
So, 1 nm = 10^-9 m
Atomic radius of C = 0.077 nm
So, atomic radius of C in m = 0.077 x 10^-9 nm.

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ANSWER

Important drawings in biology

Posted by Navya Chitturi 7 years, 1 month ago

CBSE > Class 09 > Science

3 answers

Ansh Sharma 7 years, 1 month ago

structure of neuron,and difference between human and bird

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Ananya Agnihotri 7 years, 1 month ago

Nematoda and Annelida.

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Akanksha Maurya 7 years, 1 month ago

Animal cell kingdome

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Explain law of conversation of movement

Posted by Yatish Rajan 7 years, 1 month ago

CBSE > Class 09 > Science

3 answers

Akanksha Maurya 7 years, 1 month ago

According to law of conservation of momentum the sum of momenta of the two objects before collision is equal to the sum of momenta after collision provided there is no external unbalanced force acting on them.

1Thank You

Yatish Rajan 7 years, 1 month ago

Can you explain it brifely

2Thank You

Abhishek Patel 7 years, 1 month ago

Product of mass and velocity

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Difference between relative velocity and average velocity

Posted by Kaushal Lakhotiya 4 years, 10 months ago

CBSE > Class 09 > Science

1 answers

Sia ? 4 years, 10 months ago

Differences between average velocity and relative velocity

Average velocity of a body is sum of all displacements divided by total time elapsed . Suppose a person starts from point A and after displacements in series and turnings on its paths he finally reaches a point B.
Then Net displacement = AB and if we divide it with time interval then we get average velocity as if he was travelling straight to B and relative velocity is actually composition of two velocities and is always defined with respect to an observer who is also moving.
A person moving on a cycle say with velocity v1 and another walking in the same direction with velocity v2. Now both can observe each other state of motion. But if walking man observes the cyclist he will observe a velocity v1 - v2 as if he is at rest. The cyclist will observe the man’s velocity as if he himself is at rest = v2 -v1 both are observing relative velocities but the result of measurement is different in magnitude as well as direction.
So relative velocity is never average. The two are different by definition.
In daily life the relative velocity sometimes amazes us.
Suppose a man is walking with umbrella in rain. he saw that rains are falling vertically down when he is at rest.
Now he starts to increase his speed then it happens that falling rain starts hitting his umbrella at an angle from vertical and he must turn his umbrella forward at an angle to save himself from raindrops.
So relative to man the rain appears to fall at an angle with the vertical.

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ANSWER

Why is endocytosis found in animals only

Posted by Bandana Shrivastava 7 years, 1 month ago

CBSE > Class 09 > Science

1 answers

Akanksha Maurya 7 years, 1 month ago

Endocytosis is the ingestion of material by the cells through the plasma membrane. As we know that plasma membrane is the outer covering of cell which is found in both plant and animal cell .It is a selective permeable membrane which allow in and out of protiens and substance needed in a cell. since it is found in both of them.

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ANSWER

Total time taken=4h 20min=4.33h kaise

Posted by Rajesh Kumari 7 years, 1 month ago

CBSE > Class 09 > Science