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(C) Angiospermae  is not a category

1. (A) species

2. (C) Deuteromycetes

3. (B) Three domain system of classification → Adolf Mayr

1. Viruses are acellular, highly infectious and ultramicroscopic. 

2. Viruses possess their own genetic material in the form of either DNA or RNA, but never both. The genetic material in viruses is covered by a protein coat (capsid), hence called nucleoprotein. 

3. They do not show any activity outside the body of host but once they enter their specific host cell, they start multiplying within the living host cells. 

4. Viruses lack their own metabolic machinery, they make use of the cellular machinery of the host i.e. ribosome for the synthesis of protein during their reproduction and therefore, they cause severe infection. Thus, they are called infectious nucleoproteins.

Both archaea and bacteria are prokaryotic. They differ in their cell wall structures.

• Generally, antibiotics work against any harmful bacteria, whether it is attacking humans or animals. 
• But some of them are better suited to humans while some are better for animals. This is due to the adverse effects they show in different species.
• Also, the dosages of antibiotics for humans and animals differ.

Antibiotics cure diseases by destroying or preventing the growth of harmful micro-organisms.

• Microscopic spores of fungi are present in the air. 
• If there is sufficient moisture, spores germinate on cotton fabric, gunny bags, leather, wooden items etc. 
• The fungal hyphae (fibres of the fungus) penetrate deep into the material to obtain nutrition and to reproduce. 
• This causes the materials to wear and become weak. 
• As a result, cotton fabric, gunny bags, leather and wooden items do not last long.

Correct answer is: (a) Bacteria

• Antibiotics should be taken only when prescribed by a doctor. 
• Don’t purchase any antibiotic from medical stores without a prescription from a doctor.
•  Don’t consume antibiotics on your own to treat common diseases like a throat infection, common cold or influenza. 
• Even if you feel well before completing of the prescribed course of the antibiotics, you must continue and complete it. 
• Don’t suggest to others the antibiotics which were useful to you.

• A black powder or white disc floating on the pickle or murabba are fungi. 
• Different fungal species depend on host (pickle and murabba) for their growth and reproduction. 
• During this process, fungi secretes mycotoxins which are poisonous chemicals; which ultimately spoil the food. Consuming such food can cause food poisoning. 
• Therefore, such food items are not good to eat.

1. Alexander Fleming, a professor of microbiology at St. Mary’s Hospital had cultured varieties of bacteria and fungi in petri dishes in his laboratory.

2. On 3^rd September 1928, while observing Staphylococci cultures, he made an interesting observation in one petri dish. 

3. In that petri dish, fungal colonies had grown but the area around those colonies was clean and clear, i.e. the bacteria had actually been destroyed. 

4. After further studies, he confirmed that the fungus growing there was Penicillium and its secretion had destroyed the bacterial colonies.

5. Thus, the first antibiotic – penicillin had been discovered accidentlly and this formed the basis to find cures for incurable diseases.

• Antibiotics are a group of medicines used to control inflections caused by bacteria. 
• Common cold or influenza is caused by a virus. 
• Antibiotics are not effective against viruses. 
• Therefore, antibiotics are not effective against common cold or influenza.

• When seeds coated with Rhizobial solution or powder are sown, Rhizobia enter the plantlets. 
• This is called Rhizobial inoculation. 
• Rhizobia can produce nitrogenous compounds from atmospheric nitrogen. 
• This experiment has helped in the supply of nitrogen to cereal and other crops, besides leguminous crops.
• Therefore, nowadays seeds are coated with Rhizobial solution or powder before sowing.

Correct answer is (c) Streptomyces venezuelae

The correct answer is c) momentum

a) A balloon filled with air and its mouth untied/is released with its mouth in the downward direction, it moves upwards because of the air that is present in the balloon rushes out in the downward direction. This is the equal and opposite reaction in the downward direction as the air pushes the balloon upwards. 

b) Mass of the unloaded truck, m₁ = 2000 kg

 Acceleration, a₁ = 0.5 m/s² 

Mass of loaded truck, m₂ = 2000 + 2000 = 4000 kg

 Acceleration, a₂ = ? 

m₁×a₁ = m₂×a₂ 

a₂ = 0.25 m/s²

The force exerted by the floor on her = the downward force exerted by the girl =250 N 

This is due to Newton’s third law of motion which states that to every action there is an equal and opposite reaction.

A =F/m

The correct answer is d) 500 N

Force = 10^-2 N = 0.01 N  initial velocity, u = 0

mass, m = 500 g = 0.5 kg  distance travelled, s =?    time, t = 10 sec

Force = mass × acceleration 

acceleration, a =\(\frac{force}{mass}\) = \(\frac{0.01}{0.5}\)= 0.02 m/s²

Using the equation, s = ut + \(\frac{1}{2}\) at²

 =0×10+\(\frac{1}{2}\)×0.02×10²= 1

Biogas is made up of waste products mainly gobar (cow dung). So it is known as gobar gas

Starting material for biogas is mainly cow dung. So, it is also known as gobar gas.

Bio gas is the gas formed in the biogas plant due anaerobic oxidation of organic material. But the majority of the starting material for the biogas plant is the cow dung which is known as “gobar” in Hindi Language and hence the gas formed in the biogas plant is termed as the “gobar gas”

Because fuel is used to produce heat energy by burning.

The balloon that is free to expand will displace more air as it rises than the balloon is rigid and restrained from expanding. Since the balloon is free to expand will experience more buoyant force and rises higher.  

Compass needle stays in horizontal north-south direction. At poles horizontal component H= 0; therefore there will be no effect of earth’s field on magnetic north pole and it can stay in any direction; on the other hand a dip needle points along the resultant magnetic field and at poles the resultant field is vertical; hence the needle becomes vertical.

The Garoghianian family though now poor, were famous for their honesty even when they were wealthy. They were proud of their family first, honesty next and after that, they believed in right and wrong. None of them would take advantage of anybody in the world. They would not steal. No member of the Garoghianlan family could be a thief.

(a) Yes. According to Newton's third law. The apple attracts the earth.

(b) According to Newton's second law, fora given force, acceleration a ∝ \(\frac{1}{m}\) . Here mass of an apple is negligibly small compared to earth. so we cannot see the earth moving towards and apple.

(d) 72 ms^-2 

Centripetal acceleration = \(\frac{v ^2}{r}\) = \(\frac{6^2}{0.5}\)= \(\frac{36}{0.5}\) =72 ms^-2

 (d) \(\frac{1}{sinθ}\) \(\sqrt {\frac{2h}{g}}\)

(c) Assertion is true, but the reason is false.

(a) 17.82 N 

Frictional force = µmg cos θ = 0.7 x 3 x 9.8 cos 30° = 17.82 N

(a) greater acceleration along the path AC

Force on the box due to accelerated motion of the truck 

F = ma = 40 x 2 = 80 N (in forward direction) 

Reaction on the box, F’ = F = 80 N (in backward direction) 

Force of limiting friction, f = µR = 0 .15 x 40 x 10 = 60 N 

Net force on the box in backward direction is P = F’ 

f = 80 – 60 = 20 N 

Backward acceleration in the box = a= \(\frac{p}{m}\) = \(\frac{20}{40}\) = 0.5 ms^-2

t = time taken by the box to travel s = 5 m and falls off the truck, then from

s = ut + \(\frac{1}{2}\)at² 

s = 0 x t + \(\frac{1}{2}\) x 0.5 x t² 

t = 4.47

If the truck travels a distance x during this time then x = 0 x 4.34 + \(\frac{1}{2}\) x 2 x (4.471)² 

x = 19.98 m

Force experienced by box F = ma = 40 × 2 = 80 N frictional force F_friction = µ mg = 0.15 × 40 × 10 = 60 N

∴ Net force on the box = F – F_friction = 80 – 60 = 20 N .

∴ The backward acceleration experienced by box is given by,

a = \(\frac{Net force}{mass}\) = \(\frac{20}{40}\)= 0.5 m/s²

Let‘t’ be the time taken by box to move through 5m backwards We have, 

S = ut + \(\frac {1}{2}\)at²

∴ 5 = 0 × t + \(\frac {1}{2}\) × 0.5 × t²

t = \(\sqrt20\) ≈ 4.47 s

The distance travelled by truck in t = 4.47s is

s = ut +\(\frac {1}{2}\)at² (a = 2m /s²)

s = 0 ×\((\sqrt20)\)\(\frac {1}{2}\) × 2 \((\sqrt20)^2\)

s = 20 m

The box will off the truck after 20 m from starting point.

F = 36 dyne at an angle of 60° 

F_x = F cos 60° = 18 dyne

F_x = ma_x

so a_x = \(\frac{f_x}{m}\) = 1 cm/s²

Concurrent force: 

A collection of forces is said to be concurrent, if the lines of forces act at a common point

Lami’s Theorem: 

If a system of three concurrent and coplanar forces is in equilibrium, then Lami’s theorem states that the magnitude of each force of the system is proportional to sine of the angle between the other two forces.

i.e. \(|\vec F_1|\) ∝ sin α, |\(\vec F_2\)| ∝ sin β, |\(\vec F_2\)| ∝ sin γ,

Mass of a train (m) = 3 x 10⁶ kg

Speed of the train v = 50 ms^-1

Now, the power of the engine = Force x velocity

= Fv

But, F = μR = μ mg

Hence P = μ mg v = 0.05 x 3 x 10⁶ x 10 x 50

= 7.5 x 10⁷ watt = 7.5 x 10⁴ kW

r = 1 m, ω = 4 rad s^-1, μ = 0.2

The wooden block will continue to revolve with table if force of friction is equal to or greater than the centripetal force required by it.

i.e., F ≥ {mv²}/{r}

Since F = μR = μ mg

Hence μ mg = mv²/r or, μ mg ≥ mr ω²  (∴ v = ωr)

or mrω² = μ mg or, r ≤ μg/ω²

or, r ≤ {0.2 x 9.8}/{16} ≤ 0.123 m

Thus, the block placed at 100 cm will revolve with the table.

A frame of reference is a set of three mutually perpendicular lines (direction or axes) used to specify the position of a particular or an event occurring in space.

"Any frame of reference, in which Newton's laws of motion hold and can describe the dynamics of the moving objects is called an inertial frame of reference."

In accordance with Newton's first law of motion, any system acted upon by zero net external force is an inertial frame of reference. In other words, any unaccelerated frame of reference, i.e., a frame of reference at rest or in uniform motion along a straight line (w.r.t. absolute space) is an inertial frame of reference.

Following are a few examples of inertial frame of reference:

(1) A frame of reference remaining fixed w.r.t. stars in an inertial frame of reference.

(2) A spaceship moving in outer space without spinning and with its engine cut off is also inertial frame of reference.

(3) For practical purpose, a frame of reference fixed to earth can be considered as an inertial frame. Strictly speaking, such a frame of reference is not an inertial frame of reference, because the motion of the earth around the sun is an accelerated motion due to its orbital and rotational motion. However, due to negligibly small effects of rotation and orbital motion, the motion of the earth may be assumed to be uniform and hence a frame of reference fixed to it may be regarded as inertial frame of reference.

The inertial frame of reference is important for the following reasons:

(a) All the fundamental laws of physics have been formulated in respect of inertial frame of reference.

(b) All the fundamental laws of physics can be expressed as to have the same mathematical form in all the inertial frames of reference.

(c) The mathematical and optical experiments performed in an inertial frame in any direction will always yield the same results. It is called isotropic property of the inertial frame of reference.

A frame of reference having accelerated motion is called a non-inertial frame of reference.

In an accelerated frame of reference an object experiences a fictitious force. For example, a bus moving along a circular track is an accelerated frame of reference. It is our experience that the passengers sitting in such a bus are always thrown away from the centre. This force which tends to throw the passengers away from the centre is called centrifugal force and is a fictitious force. The motion of objects in accelerated frame of reference cannot be studied by simply applying Newton's laws of motion.

The answer is 2. When a particle moves in a circular path, at each point the velocity is directed along the tangent of the circular path. Hence when string, breaks, it moves along the tangent in accordance with Newton’s 1^st law of motion.

Newton's third law of motion:- It states that every action, there is an equal and opposite reaction.

Let us consider two particles in an isolated system, their masses are m₁ and m₂ velocity are v₁ and v₂. Consider that they are moving along the same line and they interact. Their velocities change due to interaction. Thus, their momenta will also change in time Δt.

Let the change in momentum of the first particle

= ΔP₁ (Change in momentum of the second particle)

= ΔP₂

According to the law of conservation of linear momentum, in an isolated system with has no external force.

ΔP₁ + ΔP₂ = 0 or ΔP₁ = -ΔP₂

Dividing it by Δt, we have,

ΔP₂/Δt = -ΔP₁/ΔT

⇒ dP₂/dt = -dP₁/dt

⇒ F₂ = -F₁

That is force acting on m₂ = -force acting on m₁

or Action = -Reaction

This is Newton's third law of motion. When we press the sandy ground in backward direction, the sand gets pushed away and as a result, we get only very small reaction from the ground making it difficult for us to walk.

Option (b) is correct.

When the string breaks, the stone will move in the direction of the velocity at that instant. According to the first law of motion, the direction of velocity vector is tangential to the path of the stone at that instant. Hence, the stone will fly off tangentially from the instant the string breaks.

By frictional force.

Mass of the stone, m = 0.25 kg

Radius of the circle, r = 1.5 m

Number of revolution per second, n = 40/60 = (2/3)rps

Angular velocity, ω = / = 2 ………………….(i)

The centripetal force for the stone is provided by the tension T, in the string, i.e.,

T = F_Centripetal 

= mv²/r = mrω² = mr(2πn)² 

= 6.57 N

Maximum tension in the string, T_max = 200 N

T_max = mv²_max /r

v_max = √T_max x r/m

= √200 x 1.5/0.25

= √1200 = 34.64 m/s

Therefore, the maximum speed of the stone is 34.64 m/s.

Impulsive force: Forces exerted over a limited time are called impulsive forces.

Given; m = 0.1kg; y = \(0.3 t+\frac{9.8}{2} t^{2}\); F = ?
∴ Velocity v = \(\frac{d y}{d t}=\frac{d}{d t}\left(0.3 t+\frac{9.8}{2} \cdot t^{2}\right)\)
or v = 0.3 + \(\frac{9.8}{2}\) × 2t
or v = 0.3 + 9.8t
Now, the acceleration,
a = \(\frac{d v}{d t}=\frac{d}{d t}(0.3+9.8 t)\) = 0 + 9.8
or a = 9.8 m/ s²
Therefore, the force acting on the particle,
F = ma = 0.1 × 9.8
or F = 0.98 N

Mass = 100 kg 

Height = 5 m 

g = 9.8 m/s² 

PE = mgh = 4900J 

Work done = potential energy

According to this law, net linear momentum of a system remains constant in absence of external force.
According to Newton’s second law of motion
F = \(\frac{d p}{d t}\)
If external force is zero i.e., F = 0
then \(\frac{d p}{d t}\) = 0
⇒ p = constant

(a) A boy is swimming in a pond: The work done is positive because the direction of applied force and displacement are the same. 

(b) A coolie is standing with a load on his head: The work done is zero because the applied force does not cause any displacement. 

(c) Stopping a moving car by applying brakes: The work done is negative because the fore applied by the brakes acts in a direction opposite to the direction of motion of car. 

(d) Catching the ball which you friend has thrown towards you : Negative work because the force required to stop the ball, acts opposite to the displacement of the ball.