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
egestion.
(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
helpful.
(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
100
watt.
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
clearly.
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.
Work
done,
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
d.
Mollusca
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.
25.
(b)
26.
(c)
27.
(c)
28.
(b)
29.
(a)
30.
(b)
31.
(a)
32.
(b)
33. (d)
OTBA
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.
