Question

Note: Do the following work in the serence wate...
QI. It is difficult to cut cloth using a pair of scissors with blunt blades Explain
Q2. Calculate the pressure applied on a body of area 50 m' if a force of 100 N acts on it
Q3. A pendulum oscillates 60 times in 6 seconds. Find its time period and frequency
Q4. List the common varieties of polyester. Also, mention the natural fibres which are used
blending to enhance their properties.
Q5.
Give reasons:
(a) Sodium and potassium are stored in kerosene.
(b) Lemon pickle should not be stored in aluminium utensils.
(c) Copper is preferred to make electrical wires.
Q6. Name the following:
(a) a metal used to make food wrapping foil.
(b) a non-metal which is liquid at room temperature,
(c) a metal used in a thermometer.
7. Name the food preservation methods for the following:
(a) Jams and Jellies
(b) Pickles
(c) Meat and fish
Freshly collected cow's milk spoils within a few hours at room temperature but
packed in a tetra pack stays fresh for a longer period of time. Give reason.​

Answer 1

Answer 1 :

It is difficult to cut cloth with blunt pair of blunt scissor because :

$\sf{\boxed{\green{pressure=\frac{force}{area}}}}$

Area is inversely proportional to pressure .And when pressure will be less then force applied will be also less

hence,when area is more then pressure is less.

Blunt scissors have larger area as compared to sharp edge scissors . Thus ,the force applied produces a low pressure ,which make it difficult to cut cloth.

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Answer 2 :

$\sf{\boxed{\pink{pressure=\frac{force}{area}}}}$

$\sf{\implies pressure=\frac{100}{50}}$

$\sf{\boxed{\pink{\implies pressure = 2\;pascal}}}$

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Answer 3 :

$\sf{\boxed{\blue{time\;period=\frac{time\;taken}{no.\;of\;oscillations}}}}$

》time period = 6/60 = 0.1 sec

$\sf{\boxed{\blue{frequency=\frac{no.\;of\;oscillations}{time\;taken}}}}$

》frequency = 60/6=10 hertz

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Answer 4 :

Common varieties of polyester are:

PET(polythene terephthalete)

Terrycot

Terrywool

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Answer 5:

(a) Sodium and potassium are stored in kerosene

because they both are very reactive metal.So,if Sodium metal and potassium metal is kept exposed to air , it will react with the various components of the air. In order to prevent its reaction with the moisture and other gases,they are stored in kerosene.

(b) Lemon pickle should not be stored in aluminium utensils because if foodstuffs containing acid are kept in aluminium,iron or copper containers,the acid present in them react with the metal of the container slowly to form toxic salts (or poisonous salts).

(c) Copper is preferred to make electrical wire because it is good conductor of electricity.

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Answer 6 :

(a) Aluminium

(b) bromine

(c) mercury

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Answer 7 :

(a) Jams and jellies are preserved by adding sugar as preservative.Sugar reduces the moisture content from the fruit which inhibits the growth of microorganisms.

(b) Pickles are preserved by adding salt to them.

Salt does not allow bacteria or fungus to grow on it.

(c) Meat and fish is preserved by method of deep freezing. Frozen food remains unspoiled and fresh for long period.

(d) Freshly collected milk contain bacteria due to which it gets spoiled after few hours but

milk packed in tetra packs are pasteurized due to which there is no microorganisms present to spoil it.

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