CBSE Questions for Class 8 General Knowledge Basic Science Quiz 9 - MCQExams.com

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 ?
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 
  • $$2$$
  • $$\dfrac 32$$
  • $$\dfrac 12$$
  • $$113$$ There are $$N$$ coplaner vectors each of
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
  • $$\frac{\Delta A}{A} + \frac{\Delta A + \Delta B}{A- B}$$
  • $$\frac{\Delta A}{A} - \frac{\Delta A - \Delta B}{A- B}$$
  • $$\frac{\Delta A}{A} - \frac{\Delta A + \Delta B}{A- B}$$
  • $$\frac{\Delta A}{A} - \frac{\Delta A + \Delta B}{A+B}$$
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 ?
  • $$1$$
  • $$1 / 4$$
  • $$1 / 16$$
  • $$1 / 32$$
The relation between the time  of flight a projectile $$ T_{f} $$ and the time to reach the maximum height  $$ t_{m} $$ is
  • $$ T_{f} 2t_{m} $$
  • $$ T_{f} = t_{m} $$
  • $$ T_{f} = \dfrac{t_{m}}{2} $$
  • $$ T_{f} = \sqrt{2}(t_{m}) $$
  • $$ T_{f} = \dfrac{t_{m}}{\sqrt{2}} $$
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 
  • $$\sqrt{6gh}$$
  • $$\sqrt{3gh}$$
  • $$2 \sqrt{gh}$$
  • $$\sqrt{\dfrac{3}{2}} gh $$
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
1903258_533a0a22ccb542d3827d3de634579e1a.png
  • $$1.0\ kg$$
  • $$1\ kg$$
  • $$(1.0\pm 0.1)\ kg$$
  • $$(1.0\pm 0.2)\ kg$$
If the force applied is F and the velocity galance is v , then the average power developed is :-
  • $$\dfrac{F}{v}$$
  • $$\dfrac{v}{F}$$
  • $$\dfrac{Fv}{2}$$
  • $$ Fv^{2} $$
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
  • 6km/h
  • 18km/h
  • 12km/h
  • 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:-
  • $$ \dfrac{F_1}{F_2}=\dfrac{r_1}{r_2} $$ if $$ r_1 < R $$ and $$ r_2 < R$$
  • $$ \dfrac{F_1}{F_2} =\dfrac{r^2_2}{r_1^2} $$ if $$ r_1 > R $$ and $$ r_2 > R$$
  • $$ \dfrac{F_1}{F_2} =\dfrac{r_1^3}{r_2^3} $$ if $$ r_1< R $$ and $$ r_2 < R$$
  • $$ \dfrac{F_1}{F_2}= $$ if $$ r_1 < R $$ and $$ r_2 < R$$
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
  • $$ 37^{o} $$
  • $$ 60^{o} $$
  • $$ 53^{o} $$
  • $$ > 53^{o} $$
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.
  • $$N = mg\cos \theta$$
  • $$g \sin \theta = \dfrac {v^{2}}{r} \cos \theta$$
  • $$N \sin \theta - \dfrac {mv^{2}}{r} = 0$$
  • None of these
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 :
  • $$12.6 J$$
  • $$8.4 J$$
  • $$46.1 J$$
  • $$14.8 j$$
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?
  • 3 times heavier
  • 2 times heavier
  • The same weight
  • 3 times lighter
If uncertainty in the measurement of position and momentum are equal . What is uncertainty in the measurement of velocity 
  • $$\dfrac{1}{2} \sqrt{\dfrac{mh}{\pi}}$$
  • $$\dfrac{1}{2 \pi} \sqrt{\dfrac{m}{h}}$$
  • $$\dfrac{1}{2m} \sqrt{\dfrac{h}{\pi}}$$
  • None of these
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 ?
  • v
  • $$ ( \pi/4)v$$
  • $$ ( 4 / \pi)v$$
  • 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 $$ M_{3}. $$
1904111_df6faa328e544422b82ac4518d336b9f.PNG
  • $$ 2N $$
  • $$ 6N $$
  • $$ 4N $$
  • $$ 3N $$
Which one of the elements with following outer electronic configurations may exhibit the largest number of oxidation states?
  • $$3d^5 4s^1$$
  • $$3d^5 4s^2$$
  • $$3d^2 4s^2$$
  • $$3d^3 4s^2$$
Which of the following illustrations represents a pure substance? Why?
An area that is in a properly deployed state is known as?
  • Mainline
  • Baseline
  • Endline
  • Startline 
In the lecture, the first supporting detail, which defines Science, is
  • Observation, inferencing, predicting, classifying and making models
  • Science is using different skills to make models
  • One or more senses to gather info
  • None of these
Choose the true statement about steel shot versus lead shot.
  • Steel shot weighs about one-third less than lead shot.
  • Steel shot produces a larger pattern than lead shot.
  • Steel shot is softer and denser than lead shot.
  • Steel shot is more unstable in flight than lead shot.
Which two microscopes generate three-dimensional images?
  • scanning electron microscope and scanning tunneling microscope
  • transmission electron microscope and scanning electron microscope
  • scanning tunneling microscope and transmission electron microscope
  • compound light microscope and scanning electron microscope
Adaptations result from interactions between organisms and their _______.
  • behavior
  • offspring
  • gene pool
  • environment
Which of the following is a scalar quantity?
  • Displacement
  • Velocity
  • Acceleration
  • Distance
Which of the following is a unit of heat?
  • Fahrenheit
  • Energy
  • Joule
  • Celsius
The most outstanding contribution of G.N. Ramachandran in structural biology is
  • $$\alpha$$-helix structure of proteins
  • $$\beta $$-sheet structure of protein
  • Ramachandran plot
  • 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

  • only (i)
  • (i) and (ii)
  • (i) and (iv)
  • only (iv)
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
  • $$M^{0}LT$$
  • $$MLT^{-1}$$
  • $$MLT^{-2}$$
  • $$MLT$$
Which of the following is a standard unit of measurement of land ?
  • hectare
  • bigha
  • guintha
  • none
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