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CBSE Questions for Class 8 General Knowledge Basic Science Quiz 9 - MCQExams.com
CBSE
Class 8 General Knowledge
Basic Science
Quiz 9
Two object A and B are moving with velocities $$ v_{A} and v_{B} $$ respectively a,long positive x - axis If $$ v_{A} < v_{B} $$ which of the following position time graph correctly showing the velocity of A and B ?
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If $$a_1 $$ and $$a_2$$ are two non collinear unit vector unit and if $$|a_1 +a_2| =\sqrt 3$$, then the value of $$(a_1-a_2), (2a_1 +a_2)$$ is
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$$2$$
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$$\dfrac 32$$
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$$\dfrac 12$$
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$$113$$ There are $$N$$ coplaner vectors each of
Explanation
$$|a_1 +a_2|=\sqrt 3$$
$$\Rightarrow \sqrt {1+2\cos \theta}=\sqrt 3$$
$$\Rightarrow 2+2 c \theta =3$$
$$\Rightarrow 2x \theta =1\Rightarrow c\theta =\dfrac 12$$
$$(a_1 -a_2).(2a_1 +a_2)$$
$$=2a_1^2 +a_1.a_2 -2a_1.a_2-a_2^2$$
$$(\because a_1^2 =a_2^2 =a_1 .a_1 =|a_1| (a_1) \cos \theta =1)$$
$$=2-1+\dfrac {1}{2}-\dfrac {2}{2}=\dfrac {1}{2}$$
If $$Z= \frac{A}{A-B}$$ and $$A$$ and $$B$$ are measured with error $$\Delta A$$ and $$\Delta B$$ respectively, then relative error in $$Z$$, that is $$\frac{\Delta Z}{Z}$$ is equal to
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$$\frac{\Delta A}{A} + \frac{\Delta A + \Delta B}{A- B}$$
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$$\frac{\Delta A}{A} - \frac{\Delta A - \Delta B}{A- B}$$
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$$\frac{\Delta A}{A} - \frac{\Delta A + \Delta B}{A- B}$$
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$$\frac{\Delta A}{A} - \frac{\Delta A + \Delta B}{A+B}$$
Explanation
$$Z= \dfrac{A}{A-B}$$
take log both sides
$$\log z= \log \left[ \dfrac{A}{A- B} \right]$$
$$\log z = \log A - \log (A - B)$$
differentiate -
$$\dfrac{\Delta Z}{Z}=\dfrac{\Delta A}{A} - \dfrac{\Delta A - \Delta B}{A- B}$$
A man and woman are both heterozygous for the recessive allele that causes cystic fibrosis. What is the probability that their first two off spring will have the disorder ?
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$$1$$
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$$1 / 4$$
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$$1 / 16$$
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$$1 / 32$$
Explanation
Correct option: C
Explanation:
Cystic fibrosis is an autosomal recessive disorder, which means the cell should have both affected chromosome to become affected.
The Man and Female are both heterozygous with affected recessive allele i.e., $$X^CY$$ and $$X^CX$$ are crossed.
$$X^C$$
$$Y$$
$$X^C$$
$$X^CX^C$$
$$X^CY$$
$$X$$
$$X^CX$$
$$XY$$
Out of 4 only 1/4 is affected. Therefore, the probability of having the disorder in first two off spring would be 1/4 X 1/4 = 1/16.
Thus, Option C is correct.
The relation between the time of flight a projectile $$ T_{f} $$ and the time to reach the maximum height $$ t_{m} $$ is
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$$ T_{f} 2t_{m} $$
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$$ T_{f} = t_{m} $$
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$$ T_{f} = \dfrac{t_{m}}{2} $$
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$$ T_{f} = \sqrt{2}(t_{m}) $$
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$$ T_{f} = \dfrac{t_{m}}{\sqrt{2}} $$
A block of mass m is pushed towards a movable wedge of mass 2m and height h with a velocity u . All surface are smooth . The minimum value of u for which the block with reach the top of the wedge is
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$$\sqrt{6gh}$$
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$$\sqrt{3gh}$$
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$$2 \sqrt{gh}$$
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$$\sqrt{\dfrac{3}{2}} gh $$
In an experiment to determine the inertial mass of an object using Newton's second law, following graph is obtained between net force on the object and the acceleration produced in it. The mass of the object with error limits is
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$$1.0\ kg$$
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$$1\ kg$$
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$$(1.0\pm 0.1)\ kg$$
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$$(1.0\pm 0.2)\ kg$$
Explanation
using $$2^{nd} $$ Law
Feet $$=ma$$
$$m=\dfrac {f}{a}$$
at $$F=1,\ a=1$$
$$f=2, a=2$$
$$m=\dfrac {1}{1}=1\ kg$$
$$m=\dfrac {2}{2}=1\ kg$$
hence scale least count is $$0.1\ N=10\%$$
Since $$10$$ reaction is $$1$$
Least count of acceleration scale $$=0.1\ m/s^2 , 10y$$
$$m=\dfrac {f}{a}$$
$$\dfrac {\Delta m}{m}=\dfrac {\Delta a}{a}+\dfrac {\Delta f}{f}$$
$$=\dfrac {0.1}{1}+\dfrac {0.1}{1}=0.2$$
$$\Delta m=0.2 m=0.2\ kg$$
$$m=(1\pm 0.2)kg$$
If the force applied is F and the velocity galance is v , then the average power developed is :-
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$$\dfrac{F}{v}$$
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$$\dfrac{v}{F}$$
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$$\dfrac{Fv}{2}$$
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$$ Fv^{2} $$
A boat goes from point A to B downstream of a river following with a speed 6 km per hour and then comes back to point A. if time taken in upstream journey is double of that and downstream journey than speed of boat in still water is
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6km/h
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18km/h
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12km/h
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24km/h
The magnitudes of the gravitational field at distances $$ r_1 $$ and $$ r_2 $$ from the centre of a uniform sphere of radius $$ R $$ and mass $$ M $$ are $$ F_1 $$ and $$ F_2 $$ respectively. then:-
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$$ \dfrac{F_1}{F_2}=\dfrac{r_1}{r_2} $$ if $$ r_1 < R $$ and $$ r_2 < R$$
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$$ \dfrac{F_1}{F_2} =\dfrac{r^2_2}{r_1^2} $$ if $$ r_1 > R $$ and $$ r_2 > R$$
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$$ \dfrac{F_1}{F_2} =\dfrac{r_1^3}{r_2^3} $$ if $$ r_1< R $$ and $$ r_2 < R$$
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$$ \dfrac{F_1}{F_2}= $$ if $$ r_1 < R $$ and $$ r_2 < R$$
Explanation
case . $$ I (r > R) $$
$$ E= \dfrac{GM}{r^2} $$
$$ F_1=\dfrac{GM}{r_1^2} \quad and \quad F_2=\dfrac{GM}{r_2^2}$$
$$ \dfrac{F_1}{F_2}=\dfrac{r_2^2}{r_1^2}$$
case (ii) $$( r < R)$$
$$ E= \dfrac{g}{R}r$$
$$ \dfrac{F_1}{F_2} =\dfrac{r_1}{r_2}$$
Two identical billiard balls undergo an oblique elastic collision . Identically one of the balls is stationary . If the initially stationary ball after collision moves in a direction which makes an angle of $$ 37^{o} $$ with direction of initial motion of the moving ball , then the angle through which initially moving ball with be deflected is
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$$ 37^{o} $$
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$$ 60^{o} $$
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$$ 53^{o} $$
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$$ > 53^{o} $$
Explanation
Answer
Initially momentum = $$ m v \cos 37^{o} $$
as the masses of balls are same . so initially ball will come to rest along with line of impact and it will have only perpendicular velocity
then
the initially velocity ball be along $$ v \perp $$
so , angle of difletion = $$ 53^{o} $$
A ball of mass $$'m'$$ is rotating in a circle of radius $$'r'$$ with speed $$v$$ inside a smooth cone as shown in figure. Let $$N$$ be the normal reaction on the ball by the cone, then choose the wrong option.
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$$N = mg\cos \theta$$
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$$g \sin \theta = \dfrac {v^{2}}{r} \cos \theta$$
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$$N \sin \theta - \dfrac {mv^{2}}{r} = 0$$
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None of these
Explanation
$$N = mg\cos \theta$$
$$N\sin \theta = \dfrac {mv^{2}}{r}$$
$$mg\cos \theta \sin \theta = \dfrac {mv^{2}}{r}$$
$$g\sin \theta = \dfrac {v^{2}}{r\cos \theta}$$.
A particle of mass 40 g is moving in a circular orbit of radius 50 cm with frequengy 300 rpm. The work done in in increasing its frequency to 600 rpm is :
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$$12.6 J$$
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$$8.4 J$$
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$$46.1 J$$
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$$14.8 j$$
An object measures $$3 \ cm$$ by $$9 \ cm$$ by $$4 \ cm$$ and weighs $$54 \ grams$$. If another object made from the same material measures $$6 \ cm$$ by $$2 \ cm$$ and $$3 \ cm$$, what would be the weight of the second object in terms of the first object?
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3 times heavier
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2 times heavier
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The same weight
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3 times lighter
Explanation
According to question given
$$v_1= 3 \times 9 \times 4= 108$$
$$v_2 = 6 \times 2 \times 3= 36$$
$$\frac{v_1}{v_2} = \frac{w_1}{w_2}\implies w_1= 3 w_2$$
Option A
If uncertainty in the measurement of position and momentum are equal . What is uncertainty in the measurement of velocity
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$$\dfrac{1}{2} \sqrt{\dfrac{mh}{\pi}}$$
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$$\dfrac{1}{2 \pi} \sqrt{\dfrac{m}{h}}$$
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$$\dfrac{1}{2m} \sqrt{\dfrac{h}{\pi}}$$
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None of these
Explanation
$$ \Delta b = \Delta R $$
$$ \Delta b \times \Delta K \geq \dfrac{h}{4\pi} $$
$$ \Rightarrow (\Delta b)^{2} \geq \dfrac{h}{4\pi} $$
$$ \Rightarrow (m \Delta v) ^{2} \geq \dfrac{h}{4\pi} $$
$$ \Rightarrow \Delta V \geq \sqrt{\dfrac{h}{4 \pi m ^{2}}} $$
$$ \geq \dfrac{1}{2m } \sqrt{\dfrac{h}{\pi}}$$
A large number of particle are moving each with speed v having directions of motion randomly distributed .What is the average relative velocity between any two particles averaged over all the pairls ?
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v
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$$ ( \pi/4)v$$
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$$ ( 4 / \pi)v$$
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Zero
Three blocks of masses $$ M_{1} = 1kg, \;M_{2} = 2kg, \;M_{3} = 3kg $$ are placed in contact on a horizontal frictionless surface. A force $$12N $$ is applied to mass $$ M_{1}. $$ Find the contact force acting on mass $$ M_{3}. $$
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$$ 2N $$
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$$ 6N $$
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$$ 4N $$
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$$ 3N $$
Explanation
Total mass $$ = 1 + 2 + 3 = 6kg $$
So, acceleration of the blocks
$$ fnet = Mnet a $$
$$ \Rightarrow a = \frac{12}{6} = 2 m/s^{2} $$
For $$ M_{3} \rightarrow a $$
$$ N = M_{3}9 $$
$$ N = 3 \times 2 = 6N $$
Which one of the elements with following outer electronic configurations may exhibit the largest number of oxidation states?
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$$3d^5 4s^1$$
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$$3d^5 4s^2$$
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$$3d^2 4s^2$$
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$$3d^3 4s^2$$
Explanation
For transition metal elements, a general rule is $$\Rightarrow The\ max\ number\ of\ oxidation\ states = no. \ unpaired\ d-orbital\ electrons\ + \ the\ 2s\ electrons.$$
Explanation:
As noted, the maximum number of oxidation states a given transition metal is (generally) the number of unpaired $$d$$-orbitals plus the $$2\ s$$-orbital electrons. This then finds the transition elements with the higher numbers of oxidation states in the middle of the transition series.
For the question presented and written in order of Aufbau Diagram:
$$4s^1 3d^5 \Rightarrow 4s\uparrow 3d\uparrow \uparrow \uparrow \uparrow \uparrow 4s\uparrow 3d\uparrow \uparrow \uparrow \uparrow \uparrow \Rightarrow 6\ oxidation\ states$$
$$4s^2 3d^5 4s^2 3d^5 \Rightarrow 4s\uparrow \downarrow 3d\uparrow \uparrow \uparrow \uparrow \uparrow 4s\uparrow \downarrow 3d\uparrow \uparrow \uparrow \uparrow \uparrow \Rightarrow 7\ oxidation\ states$$
$$4s^2 3d^2 \Rightarrow 4s\uparrow \downarrow 3d\uparrow \uparrow 4s\uparrow \downarrow 3d\uparrow \uparrow \Rightarrow 4\ oxidation\ states$$
$$4s^2 3d^3 \Rightarrow 4s\uparrow \downarrow 3d\uparrow \uparrow \uparrow 4s\uparrow \downarrow 3d\uparrow \uparrow \uparrow \Rightarrow 5\ oxidation\ states$$
Example:
Iron has $$4$$ unpaired electrons and $$2$$ paired electrons. To find one of its oxidation states, we can use the formula:
Oxidation State of $$Fe = 4 + 2 = +6$$
Indeed, $$+6$$ is one of the oxidation states of iron, but it is very rare. Other possible oxidation states for iron includes: $$+5,\ +4,\ +3,$$ and $$+2.$$
Here are some oxidation states of elements in the $$1st$$ Transition Series
Which of the following illustrations represents a pure substance? Why?
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Explanation
Option $$C$$
Explanation:
A pure substance contains only the ONE type of atom or molecule. Pure substances can be elements or compounds.
A depicts at least two types of substance, a diatomic molecule, $$X_2$$, and a heteronuclear diatomic, $$AX; B$$ depicts single atoms, and another heteronuclear diatomic; $$D$$ depicts the same as $$B$$.
For $$C$$, however, only the one type of heteronuclear diatomic is present. Reasonable examples would include $$HX$$ or $$CO$$.
An area that is in a properly deployed state is known as?
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Mainline
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Baseline
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Endline
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Startline
In the lecture, the first supporting detail, which defines Science, is
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Observation, inferencing, predicting, classifying and making models
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Science is using different skills to make models
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One or more senses to gather info
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None of these
Explanation
Science is using different skills to make models.
Choose the true statement about steel shot versus lead shot.
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Steel shot weighs about one-third less than lead shot.
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Steel shot produces a larger pattern than lead shot.
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Steel shot is softer and denser than lead shot.
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Steel shot is more unstable in flight than lead shot.
Which two microscopes generate three-dimensional images?
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scanning electron microscope and scanning tunneling microscope
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transmission electron microscope and scanning electron microscope
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scanning tunneling microscope and transmission electron microscope
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compound light microscope and scanning electron microscope
Adaptations result from interactions between organisms and their _______.
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behavior
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offspring
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gene pool
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environment
Which of the following is a scalar quantity?
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Displacement
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Velocity
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Acceleration
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Distance
Explanation
(D) Distance is the scalar quantity.
Which of the following is a unit of heat?
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Fahrenheit
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Energy
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Joule
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Celsius
Explanation
(C) As heat is a form of energy so the unit of energy is Joule. So unit of heat is Joule.
The most outstanding contribution of G.N. Ramachandran in structural biology is
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$$\alpha$$-helix structure of proteins
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$$\beta $$-sheet structure of protein
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Ramachandran plot
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Both 1 and 2
Which of the following can sometimes be 'zero' for a moving body?
(i) average velocity
(ii) distance travelled
(iii) average speed
(iv) displacement
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only (i)
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(i) and (ii)
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(i) and (iv)
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only (iv)
Explanation
Distance
is the length of the actual path covered by a
moving body
. This implies that the
distance travelled
by a
moving body
and also its
average speed can
never be
zero
at any point of time. So, option C is correct.
The expression for the force is given by $$b+\dfrac{c}{t^{3}}$$, where $$'b'$$ and $$'c'$$ are some physical quantities and $$'t'$$ is the time. Then the dimensions of $$'c'$$ are
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$$M^{0}LT$$
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$$MLT^{-1}$$
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$$MLT^{-2}$$
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$$MLT$$
Which of the following is a standard unit of measurement of land ?
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hectare
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bigha
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guintha
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none
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