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This section includes 7 InterviewSolutions, each offering curated multiple-choice questions to sharpen your Current Affairs knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Show that the velocity of an object released from rest at infinity reaches the earth with a velocity equal to the escape velocity. |
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Answer» Solution : By the principle of conservation of energy for the OBJECT, TE at INFINITY = TE at the surfece of the earth (KE+PE) at infiniy (KE+PE) at the surface of the earth. As the body is RELEASED from rest at infinity, its KE at inifinity is zero and its PE at infinity is also zero. If v is its velocity on reaching the earth its KE becomes equal to `1/2mv^2` and PE=`(GMm)/R` `therefore 0+0=1/2mv^2 -(GMm)/R , 1/2v^2=(Gm)/R rArr` The velocity of the object `V=sqrt((2GM)/R)= V_e` . |
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| 2. |
Two particles of different masses collide head on. Then for the system |
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Answer» Loss of K.E is zero, if it were PERFECT ELASTIC collision |
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| 3. |
A physical quantity P is described by the relation P=a^2b^2c^3d^(-4)If the relative errors in the measurement as a, b, c and d respectively, are 2%, 1%, 3%, and 5%, then the relative error in P will be : |
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Answer» 0.25 |
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| 4. |
Are dimension of mass and weight equal ? |
| Answer» Solution :No, dimension of MASS is (M) and dimension of WEIGHT is `[M^(1)L^(1)T-^(-2)]`. | |
| 5. |
A person of mass M = 90 kg standing on a smooth horizontal plane of ice throws a body of mass m = 10 kg horizontally on the same surface. If the distance between the person and body after 10 seconds is 10 metres, the K.E. of the person (in Joules) is |
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Answer» `0.45` |
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| 6. |
Assertion : Small water drops are sperical while bigger water drops are not. Reason : In small water drops surface tension forces dominate while in bigger water drops gravity forces dominate. |
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Answer» If both Assertion and REASON are CORRECT and Reason is the correct explanation of Assertion. |
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| 7. |
The radius of the earth is about 6400 km and that of mars is about 3200 km. The mass of the earth is about 10 times that of mars. If an objects weighs 200 N on the surface of earth its weight on the surface of mars would be |
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Answer» 40 N |
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| 8. |
When a body is projected vertically up, at a point .P. in its path, the ratio of potential to kinetic energies is 3 : 4. If the same body were to be projected with two times the initial velocity, the ratio of potential to kinetic energies at the same point is |
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Answer» `3:25` |
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| 9. |
A disc of radius Y is removed from the disc of radius .R. then (a) The minimum shift in centre of mass is zero (b) the maximum shift in centre of mass cannotbe greater than (r^(2))/((R+r)) (c) Centre of mass must lie where mass exists (d) the shift in centre of mass is(r^(2))/((R+r)) |
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Answer» only a and B are CORRECT |
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| 10. |
In the figure shown, the two identical balls of mass M and radius R each, are placed in contact with each other on the frictionless horizontal surface. The third ball of mass M and radius R//2, is coming down vertically and has a velocity = v_(0) when it simultaneously hits the two balls and itself comes to rest. Then, each of the two bigger balls will move after collision with a speed equal to |
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Answer» `4v_(0)//SQRT(5)` ` -Jsintheta=0-Mv_(0)` `Jsintheta=Mv_(0)`………II from eqn i and ii `TANTHETA=v_(0)/v` ………..iii  From `/_\AOC` `tantheta=(sqrt5R/2)/(R/2)=sqrt(5)` `sqrt(5)=v_(0)/vimpliesv=v_(0)/sqrt(5)` |
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| 11. |
If error in measurement of radius of sphere is 1%. What will be the error in measurement of volume? |
| Answer» SOLUTION :`3%` | |
| 12. |
(A) : Steel is more elastic than rubber. (R) : Under given deforming force, steel is deformed less than rubber. |
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Answer» Both .A. and .R. are TRUE and .R. is the correct explanation of .A. |
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| 13. |
Explain the concept of inertia write two exampleseach inertia of motion inertia of rest and inertia of direction |
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Answer» Solution :Inbilityof objects to MOVE on itsown ofchange its stateof motionis calledinertiaInertia meansresistanceto changeits stable. EXAMPLEFOR Inertiaof rest: Astationarybusstartsto movethe passengersexperience a suddenbackwardpush . Examplefor Inertiaof motion :The passengerin a running bustendsto leanforward whenthe busstopssuddenly Examplefor Inertiaof direction : When astonetiedto a stringis inwhiringmotionand if the stringis cutsuddenly the stonewill movetangential to the circle. Rotatingwheelsof avehiclethroughoutmudin a TANGENTIAL direction . thisis thereasonthatmudguardsare providedoverthe wheels. |
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| 14. |
A ball is projected vertically down with an initial velocity from a height of 20 m on to a horizontal floor. During the impact it loses 50% of its energy and rebounds to the same height. The velocity of projection is (g=10 ms^(-2)) |
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Answer» `20 ms^(-1)` |
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| 15. |
Explain surface tension in the context of potential energy. |
Answer» Solution :The LIQUID stays together because of ATTRACTION between molecules.  Schematic picture of molecules in a liquid , at the surface and balance of forces. (a) Molecule inside a liquid . Forces on a molecule due to others are shown . Direction of arrows indicates attraction of repulsion .(b) Same , for a molecule at a surface. (C ) Balance of ATTRACTIVE (A) and REPULSIVE (R ) forces. |
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| 16. |
Two small spheres of masses 10kg and 30 kg are joined by a rod of length 0.5 m and of negligible mass. The M.I of the system about a normal axis through centre of mass of the system is |
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Answer» `1.875 KGM^(2)` |
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| 17. |
Two metalic wires of same length an d same cross - section but different Young modulus are pulled by same force . Which wire will be elangated more ? |
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Answer» SOLUTION :`Y = (F/A)/(/_\l/L)` if LA and F are same `Y PROP (/_\l/L)` |
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| 18. |
A sound source and listener are both stationary and a strong wind is blowing. Is there a Doppler effect? |
| Answer» Solution :YES, It does not matter whether the sound source or the transmission MEDIA are in motion, vibrations will be compressed in the DIRECTION of convergence and DILATED in the direction of divergence . | |
| 19. |
Let V and E represent the gravitational potential and field at a distance r from the centre of a uniform solid sphere .Consider the two statements. (A)The plot of V against r is discontinuous (B)The plot of E aginst r is discontinuous |
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Answer» Both A and B are CORRECT |
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| 20. |
Percentage error in measurement of (125pm0.5) cm will be………. |
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Answer» `0.1%` `=(DELTAL)/(L)XX100` `=(0.5)/(125)xx100=0.4%` |
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| 21. |
In a certain region of space a uniform and constant electric field and a magnetic field parallel to each other are present. A proton is fired from a point A in the field with speed V=4xx10^(4)m//s at an angle of alpha with the field direction. The proton reaches a point B in the field where its velocity makes an angle betawith the field direction. If (sinalpha)/(sinbeta)=sqrt3. Find the electric potential difference between the points A and B. Take mp (mass of proton) =1.6xx10^(-27)kg and e (magnitude of electronic charge) =1.6xx10^(-19)C. |
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Answer» 16 V |
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| 22. |
A rectangular block of mass m and area of cross - section A floats in a liquid of density rho. If it is given a small vertical displacement from equilibrium, it undergoes oscillation with a time period T. |
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Answer» `Tpropsqrt(m)` |
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| 23. |
Specify the number of significant figures in the following measurements : (i) 5.000kg (ii) 3500 m (iii) 0.070s. |
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Answer» SOLUTION :(i) Four: 5,0,0,0 are all SIGNIFICANT (ii) Four : 3,5,0,0 are all significant (iii) TWO, only 7 and 0 after it, are significant |
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| 24. |
Identify the correct statement. In the absence of external force,(a) the kinetic energy associated with the motion of centre of mass is conserved(b) centre of mass is not accelerated(c ) the centre of mass always move in curved line(d) centre of mass must be at rest |
| Answer» Answer :A | |
| 25. |
Water is flowing in a horizontal tube. The pressure at a point is 0.01m of Hg at which the velocity is 0.8 ms^(-1). Find the pressure at a point where the velocity is 0.9 ms^(-1) |
| Answer» SOLUTION :0.009363m of HG | |
| 26. |
The density of mercury is 13600 kg m^(-3). Its value in CGS system will be |
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Answer» `13.6 g cm^(-3)` |
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| 27. |
Two masses m_(1) and m_(2) are connected by a spring of force constant k and are placed on a frictionless horizontal surface. Initially the spring is stretched through a distance x_(0), when the system is released from rest. Find the distance moved by two masses before they again comes to rest. |
Answer» Solution : Blocks again come to rest when SPRING is COMPRESSED by `x_(0)`. SINCE no external force is acting on the system, so there is no change in the position of c.m. of the system. i.e. `Deltax_(CM)=0`. Let mass `m_(1)` displaces by `Deltax_(1)` and `m_(2)` displaces by `Deltax_(2)`, then We have `Deltax_(1)+Deltax_(2)=2x_(0)`............`(i)` and `Deltax_(cm)=(m_(1)Deltax_(1)+m_(2)Deltax_(2))/(m_(1)+m_(2))` As `Deltax_(cm)=0` `:.(m_(1)Deltax_(1)+m_(2)Deltax_(2))/(m_(1)+m_(2))=0`.......`(ii)` After solving equation `(i)` & `(ii)`, we get `Deltax_(1)=(2m_(2)x_(0))/(m_(1)+m_(2))`, `Deltax_(2)=(2m_(1)x_(0))/(m_(1)+m_(2))` |
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| 28. |
Dispersion of light is shown in the following diagram, select the CORRECT one. |
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Answer»
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| 29. |
A river is flowing due east with a speed 3ms^(-1). A swimmer can swim in still water at a speed of 4ms^(-1). If swimmer starts swimming due north, then the resultant velocity of the swimmer isa) 3 m/sb) 5 m/sc) 7 m/sd) 2 m/s |
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Answer» 3 m `s^(-1)`  Here, Velocity of water FLOWING in river, `vecv_(r) = 3 m s^(-1)` Velocity of swimmer in STILL water, `v_(s) = 4 MS^(-1)` From figure, The resultant velocity of the swimmer is `V = sqrt(v_(s)^(2) + v_(r)^(2)) = sqrt((4)^(2) + (3)^(2)) = sqrt(25) = 5ms^(-1)` |
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| 30. |
Obtain the position of centre of mass of a thin rod of uniform density. |
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Answer» Solution :Homogeneous body means a body with uniformly distributed mass. Let us consider a thin rod, whose width and breadth (in case of cross-section of the rod is RECTANGULAR) or radius (In case of the cross section of the rod is cylindrical) is MUCH smaller than its length. Taking the origin to be at the geometric centre of the rod and X-axis to be along the length of the rod, for every element dm of the rod at `+x` there is an element of the same mass dm located at `-x`.  The net contribution of every such pair to the integral and HENCE the integral. `intxdm` itself in zero. `THEREFORE` Centre of mass of rod, `X=(1)/(M)intxdm` but `dm=lambdadx` where `lambda` = mass per unit length = `(M)/(L)` `=(M)/(L)dx` where L = length of rod, `therefore X=(1)/(M)intx(M)/(L)dx` `=(1)/(L)underset(0)overset(1)intxdx` `=(1)/(L)[(x^(2))/(2)]_(0)^(L)` `=(1)/(L)[(L^(2))/(2)]` `=(1)/(2)`. Hence, centre of mass of thin rod of uniform density lies at midpoint of the length of rod means at its geometric centre. Centre of mass of homogeneous ring, disc and spheres can be found in this way and above all bodies their centre of mass coincide with their geometric centre. Position of centre of mass of bodies of regular shape : 
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| 31. |
Two blocks of masses 2m and m are in equilibrium a shown in the figure. Now the string between the blocks is suddenly broken. The accelarations of the blocks A and B respectively, at that instant are |
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Answer» g and g  when the STRING breaks, T will suddenly disappear, For B, T-2mg=2ma 3mg-2mg=2ma [T=3 mg] a=g/2 |
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| 32. |
The gravitational field in a region is given by E = 10(hat(i) + hat(j))N//kg. The work done by an external agent to slowly shift a particle of mass 2kg from the point (0,0) to a point (5m, 4m). |
| Answer» ANSWER :D | |
| 33. |
If we change the axis of rotation does the magnitude of angular momentum change? |
| Answer» SOLUTION :Yes. When the axis of rotation changes, `vecr and vectheta` also changes and HENCE angular MOMENT changes. | |
| 34. |
A gas expands from 10 litre to 20 litre at a constant pressure of 2 atmospheres. What is the work done by the gas during the expansion ? |
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Answer» <P> Solution :`P=2" atmospheres"=2xx1.013xx10^(5)= 2.026xx10^(5) NM^(2)``V_(1)= 10" litre" = 10xx10^(3) cm^(3) = 10^(-2) m^(3)`, `V_(2)=20 "litre" = 2xx10^(-2) m^(3)`. WORK DONE = `P(V_( 2)-V_(1)) = 2.026xx10^(5)` `(2xx10^(-2)-1xx10^(-2)) = 2.026xx10^(3) J.` |
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| 35. |
A metre scale is moving with uniform velocity.This implies |
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Answer» the force acting on the scale is zero, but a TORQUE about the CENTRE of mass can act on the scale. By usingNewton secondlawof MOTION as scalemoveswithuniformvelocityhence `Deltav=0` `Delta p = m Delta v = m ( 0) = 0` `F=(Delta p )/( Delta t ) = 0` Henceall the partsof scalemovingwithuniformvelocityhencetotalforceis zero. `:.`Torque willbe zero. |
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| 36. |
Consider a uniform square plate of side 'a' and mass 'm'. The moment of inertia of this plate about an axis perpendicular to its plane and passing through one of its corner is |
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Answer» `(5)/(6)ma^(2)` |
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| 37. |
The radius of the earth is about 6400km and that of mars is about 3200km. The mass of the earth is about 10 times that of mars. If an object weighs 200 N on the surface of earth its weight on the surface of mars would be |
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Answer» 40 N |
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| 38. |
The maximum tension in the string of a pendulum is two times the minimum tension. Let theta_(0) is |
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Answer» `1/2` |
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| 39. |
Role of DNA in heredity is the basis of …………. |
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Answer» |
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| 40. |
A spring which is initially in un-streatched condition, is first stretched by a length x and again by a further length x. The work done in the first case W_(1) is one third of the work done in second case W_(2). True of false ? |
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Answer» Solution :The AMOUNT of work done to stretching distance X `W_(1)=1/2k^(2) thereforek=(2W_(1))/x^(2)` Total work done in stretchig the spring through a distance `2x "is" W_(2)=1/2k(2x)^(2)` `W_(2)1/2((2W_(1))/ x^(2))4x^(2)=4W_(1)` Extra work REQUIRED to stretch the additional x distance is `W=W_(2)-W_(1)=4W_(1)-W_(1)=3W^(1)` `THEREFORE W_(1)=1/3W` Hence it is true. |
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| 41. |
A disc of mass m_(1) radiu s r is released from in the fig shown. If the cylinder is o the verge of slipping as well as toppling then coefficient of friction between cylinder and table surface is : |
| Answer» ANSWER :A | |
| 42. |
"A parachute descends slowly " Why ? |
| Answer» Solution :DUE to larger SURFACE AREA, the force of friction is greater. So. | |
| 43. |
When milk is churned cream gets separated due to |
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Answer» centripetal force |
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| 44. |
Assertion : We can not move even a finger without disturbing all the stars. Reason : Everybody in this universe attracts every other body with a force which is inversely proportional to the square of distance between them. |
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Answer» Both Assertion and REASON are TRUE and Reason is the correct EXPLANATION of Assertion |
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| 45. |
According to , three cars P, Q and R are at three points along the x-axis at a given moment. Now the car p starts its motion towards P_(1) parallel to the y-axis with a uniform velocity v. Again, R is in motion paraIIeI to the y-axis along "RR"_(1) with uniform acceleration a. If the car Q too moves paraIIeI to the y-axis then under what condition will aII of them remain coIIinear? Given PQ = QR. |
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Answer» <P> Solution :LET the time be t after which P and R are at `P_(1)` and `R_(1)` respectively.`:. ""PP_(1) = vt " ""and" " ""RR"_(1) = (1)/(2)at^(2)` According to the question after time t, Q will be at `Q_(1)`. From the figure we have , `(PP_(1))/(PM) = ("QQ"_(1))/(QM)=("RR"_(1))/(RM)=k` (say) `:. "" PP_(1)= k.PM = k(PQ+QM)` `"QQ"_(1) = k.QM` and `"RR"_(1)=k.RM = k(QR-QM)` `:."""PP"_(1)-"RR"_(1)=k.(QM+QM)" "[becausePQ=QR]` = 2 k.QM `:.""k.QM= ("PP"_(1)-"RR"_(1))/(2)` `:. """QQ"_(1) = k.QM` `=("PP"_(1)-"RR"_(1))/(2)=(PP_(1))/(2)-("RR"_(1))/(2)=(vt)/(2)-(1)/(4)at^(2)` `:."" "QQ"_(1)=((v)/(2))t-(1)/(2)((a)/(2)).t^(2)` Comparing equation (1) with s = ut `-(1)/(2)at^(2)` , we can say that to remain in the same straight line joining the other two cars, the initial velocity of the car Q must b `(v)/(2)` along the positivey-axis and it should move with a retardation `(a)/(2)`. |
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| 46. |
Water rises to a height of 16.3cm in a capillary ofheight 18 cm above the water level. If the tube is cut at a height of 12 cm: |
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Answer» water will come as a fountain from the CAPILLARY TUBE |
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| 47. |
In a ballistics demonstration a police officer fires a bullet of mass 50.0 with speed 200 ms^(-1) on soft plywood of thickness 2.00 cm . The bullet emerges with only 10 % of its initial kinetic energy. What is the emergent speed of the bullet ? |
| Answer» SOLUTION :`v_(F) = 94.87 MS^(-1)` | |
| 48. |
Molecular forces exist between the molecules of a liquid in a container. The molecules on the surface have unequal force leading to a tension on the surface. If this is not compensated by a force, the equilibrium of the liquid will be difficult task. This leads to an excess pressure on the surface. The nature of the meniscus can inform us of the direction of the excess pressure. The angle of contact of the liquid decided by the forces between the molecules, air and container can make the angle of contact.If the excess pressure in a soap bubble is P, the excess pressure in an air bubble is |
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Answer» P/2 |
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| 49. |
Attempt to formulate your 'moral' views on the practice of science. Imagine yourself stumbling upon a discovery, which has great academic interest but is certain to have nothing but dangerous consequences for the human society. How, if at all, will you resolve your dilemma ? |
| Answer» Solution :A scientist aims at TRUTH. A scientific discovery reveals a truth of nature. So, any discovery, good or bad for mankind, must be made public. A discovery which appears dangerous today may BECOME useful to the mankind some time later. In order to prevent misuse of scientific technology, we must build up a strong public opinion. SCIENTISTS should in FACT take up TWO roles - to discover truth and to prevent its misuse. | |
| 50. |
Molecular forces exist between the molecules of a liquid in a container. The molecules on the surface have unequal force leading to a tension on the surface. If this is not compensated by a force, the equilibrium of the liquid will be difficult task. This leads to an excess pressure on the surface. The nature of the meniscus can inform us of the direction of the excess pressure. The angle of contact of the liquid decided by the forces between the molecules, air and container can make the angle of contact.In a meniscus of radius r, with excess pressure P, atmospheric pressure P_0 , the force experienced is |
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Answer» <P>`(p-p_0) PI r^2 ` |
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