Answer key - CLASS 9 science
1. A compound prepared by any method contains the same elements in the fixed ratio by mass is
the law of constant proportion.
2. A false body cavity between body wall and gut, e.g. in roundworms.
3. It is defined as persistence of sound due to its multiple reflections.
4. Four main feature of phylum coelenterate are:
(a) These animals live in water.
(b) The body has a sac like body cavity with a single opening to the outside for ingestion and
(c) These are the first multicellular animals which possess tissue level organization with
distinct division of labour.
(d) The body is made of two layers of cells – one makes up cells on the outside of the body
and the other makes up inner lining of body.
5. Energy is defined as capacity of an object to do work. SI unit of energy is joule. Energy
possessed by a body is said to be 1 joule if it can displace an object by 1 m by applying a force
of 1N in the direction of force.
6. (a) Thomson’s model of an atom
(i) Atom consists of positively charge uniformly distributed.
(ii) Electrons are embedded in positively charged sphere like seeds in watermelon.
(iii) Atom is neutral.
(iv) Mass of an atom is uniformly distributed.
(b) (i) Most of α-rays passed through gold foil undeviated.
(ii) some α- rays deviated through larger angles.
7. The range of variations that we see in life-forms around us are:
(a) Size: There is a lot of variation in the size of organism that we see. The size of microscopic
bacteria is few micrometers while the size of blue whale is about 30 meters and height of
red wood tree s of California is about 100 meters.
(b) Life Span: There is lot of variation in the life span of organisms. The life span of insects like
mosquito is only a few days whereas , the life span of a pine tree is thousand of years.
(c) Colour: There is a lot of variations seen in colour. Worms are colorless or transparent
whereas flowers and birds are brightly coloured.
8. Groups of causing organism are:
(a) Viruses (b) Bacteria (c) Fungi (d) Protozoan’s (e) Multicellular Worms
9. The means of spread of infectious disease are
Direct contact with infected person
By air,food or water
By mosquitoes or insects and other vectors
By rabid animals
Through sexual contact
Through blood transfer
10. Diseases spread through water when the excreta from someone suffering from an infectious
disease such as cholera , gets mixed with drinking water used by people living nearby. The
Cholera causing microbes will enter new hosts through the water they drink and cause disease in them. Such diseases are more likely to spread in the absence of safe supply of drinkin water.
11. p.no.166 in textbook, sample problem e.g. 12.1
12. Bats emit high frequency ultrasound squeaks while flying and listen to the echoes produced by the reflection of their squeaks from the prey like a flying insect. From the time taken by the echo to be heard, bats can judge the distance of the insect and hence catch it.
13. a. Energy due to the motion of a body is called kinetic energy.
K.E. = ½ mv2
b. m=2Kg, t=5 s
Velocity after 5 s(v)=0+ 10x5=50 m/s
Therefore K.E.=1/2 x 2 x (50)2 =2500 joule=2.5 KJ.
14. (a) Anju is brave but careless to some extent. Manju however is caring, co-operating and
(b) Potential (at extremes) to kinetic (at mean position) and vice versa.
(c) Kinetic Energy of swing.
15. (a ) 1 kWh=3.6 x 106 joule
(b) M=2.5Kg, g=10m/s2 , h=20m , n=10
Power(P)=nmgh/t = (10x2.5x10x20)/50
16. a. The property of sound to get reflected from a surface of solid or liquid, and to persist on our
brain for a very short time leads to formation of echoes.
b. Reflection of sound from parabolic concave back walls spread the sound uniformly
throughout the room , even to the last corner. So, the audiences at back portion also listen
c. No, as there is no atmosphere in the moon, sound can’t travel on the surface of the moon.
17. AIDS is considered a syndrome and not a disease because AIDS causing virus- HIV comes into
the body via the sexual organ or any other means like blood transfusion and spread to lymph
nodes all over the body. The virus damages the immune system of the body and the body can
no longer fight off even minor infections. Instead, every small cold can become pneumonia, or
minor gut infection can become severe diarrhea. The effect of disease becomes very severe
and complex, at times killing the person from AIDS. Hence there is no specific disease
symptoms for AIDS but it results in a complex diseases and symptoms.
18. We know that speed of wave, v= Length Travelled/ Time taken
=> v=λ/T=λf as f=1/T
V= 340 ms-1
(a) λ=v/f= 340/256=1.33m
(b) f=v/ λ=340/0.85=400 Hz
19. (a) Energy by virtue of motion of body is called its kinetic energy. Consider a mass m moving
with a speed u and a force F applied on it, which changes its velocity to displacing by s.
W=ma.((v2-u2)/2a) ( W=F.s)
So, W=1/2 m (v2-u2)
If initial velocity, u is zero, then w=1/2 mv2
K. E. can’t be negative as it has all positive quantities. It is scalar quantity, so no direction is
taken in to consideration.
(b) m=1200 Kg, s=40 m and t=5 s
Using s=ut + ½ at2 and u=0;
We get a= 2s/t2 = (2x40)/ (5)2 = 80/25 m/s2
Work done, = F.s= ma x s= 1200 x 80/25 x 40
= 153600 joule=153.6 K
20. a. the no. of atoms constituting a molecule is known as atomicity. Atomicity of P is 4 (2)
b. atoms are indivisible particles which cannot be created or destroyed during a chemical reaction.(1)
c. it means an atom of sulphur is 32 times heavier than 1/12th of the mass of 1 carbon – 12 atom.(1)
d. one molecule has 5 atoms.(1)
21. a. coelom is body cavity, well developed organs can be accommodated within this.
b. pin worms, round worms
c. coelomic cavity is blood filled, open circulatory system
blood doesnot flow in well defined vessels
in these coelomic cavity is reduced.2
22. Mass of (copper sulphate + sodium sulphide) = Mass of (copper sulphide + sodium sulphate)
15.9 g + 7.8 g = 9.5 g + x
X = 23.7 g -9.5 g = 14.2 g
23. The stages during the life cycle of mosquito is :
(a) eggs (b) Larva (c) Pupa (d) adult
24. an object will sink in a liquid if its density is more than that of the liquid. So, the density of liquid B is more than that of A.
1. Accumulation of wastes increases the number of insect vectors like flies, mosquitoes etc., scavengers such as stray dogs, pigs and rats. These spread dangerous diseases. It also generates bad odour and causes pollution.
2. In Mizoram. TSC was introduced in 2002. Emphasis has been laid on information, education and communication components to change the behavior of the targeted population, by creating awareness about health education.the programme is being implemented with focus on community-led and people centred initiatives. The village water and sanitation committee plays an effective role in absorbing new ideas and concepts. Through the TSC, the consciousness of the community is being transformed towards health and hygiene practices.
The generation of demand for sanitation facilities motivated the targeted audiences and they are willing to pay their share in the project. Thus, the physical implementation of this programme has made remarkable achievements in converting dry toilets into pour flush toilets, and construction of septic tanks. The programme has made a highly positive impact, especially in the rural areas.
3. A. water harvesting during rains to recharge ground water and avoid run offs as wastage.
b. hydro-geological survey to identify over exploited areas.
c. artificial recharging of ground water in such areas.
d. transfer of surplus water to water deficit basins by interlinking of rivers
e. restoring traditional methods of rain harvesting and storing water
f. the use of three R’s when using water for domestic and industrial consumption
g. mass awareness programs through public/private agencies
h. integrated watershed plan for drinking, irrigation and industrial uses
i. prevention of clearing of forest areas and increase of tree cover as flood control measures.