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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. |
Current density and electric current are related by I =_______ |
| Answer» Solution :`int_svecJ.vec(DA).R"<<"NR R">>"nr` | |
| 2. |
A ball is thrown vertically upward.Which of the following plots represents the speed-time graph of the ball during its flight if the air resostance is not ignored? |
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Answer»
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| 3. |
A parallel plate capacitor is connected to a battery. The plates are pulled apart with a uniform speed. If x is the separation between the plates, the time rate of change of electrostatic energy of capacitor is proportional to |
| Answer» ANSWER :A | |
| 4. |
Assertion : A charged capacitor is disconnected from a battery. Now, if its plate are separated further, the potential energy will fall. Reason : Energy stored in a capacitor is equal to the work done in charging it. |
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Answer» If both ASSERTION and REASON are TRUE and Reason is the CORRECT EXPLANATION of Assertion. |
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| 5. |
In the given circuits for ideal diode , the current through the battery is |
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Answer» `0.5` A |
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| 6. |
A circular converging lens, with diameter d = 32 mm and focal length f = 24 cm, forms images of distant point objects in the focal plane of the lens. The wavelength is lambda = 550 nm. What is the separation Ar of the centers of the images in the focal plane? (That is, what is the separation of the central peaks in the two intensity-versus-position curves?) |
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Answer» Solution :Calculations: From either triangle between the lensand the screen, we SEE that `tan theta_(i) // 2 = Delta x // 2f`. Rearranging this equation and making the APPROXIMATION `tan THETA ~~ theta`, we find `Delta x =f theta,""(35-65)` where `theta_(i)` is in radian measure. We then find `Delta x =(0.24 m)(2.1 xx 10^(-5) RAD) = 5.0 mu m`. (Answer) |
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| 7. |
In the given circuit as shown below, calculate the magnitude and direction of the current |
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Answer» SOLUTION :Effective RESISTANCE of the circuit is `R_("eff")=2+2+1=5Omega` `therefore"total current in the circuit is I"=(V_(1)-V_(2))/(R_("eff"))` `i=(10-5)/(5)=1A` Since the cell of larger emf DECIDES the direction of flow of current, the direction of current in the circuit is from A to B through e |
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| 8. |
If l_1,l_2,l_3 are the lengths of the emitter, base and collector of a transistor, then : |
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Answer» `l_3 LT l_2 lt l_1` |
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| 9. |
When a current drawn from a battery is 0.5A, its terminal potential difference is 20V. And when current drawn from it is 2.0A, the terminal voltage reduces to 16V. Find out, e.m.f and internal resistance of the battery. |
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Answer» Solution :We known `V=E-Ir`, `I=0.5A, V=20` Volt, we have `20=E-0.5r"…..(i)"` `I=2A, V=16" Volt, we have "16=E-0.2r"…..(ii)"` From EQS (i) and (ii) `2E-r=40` and `E-2r=16` SOLVING we GET `E=21.3V, r=2.675Omega`. |
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| 10. |
On inserting a dielectric between the plates of a capacitor its capacitance is observed to increase 5 times. What is the relative permittivity of the . dielectric. |
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Answer» |
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| 11. |
A nuclear reactor has a power of 16 kW. If the energy released per fission is 200 MeV, the number of fissions per second is |
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Answer» `5xx10^16` |
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| 12. |
Which one is correct pair ? |
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Answer» PRINCIPLE of VELOCITY selector - Bain bridge mass spectrograph |
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| 13. |
Which of following is more appropriate material for making an electromagnet ? |
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Answer» Copper |
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| 14. |
A bullet of mass (M) hits a block of mass (M) the transfer energy is maximum then: |
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Answer» M'=M |
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| 15. |
The charges in a electrostatics field are analogous to ............Ina gravitational field. |
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Answer» |
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| 16. |
The amplitude (A) of damped oscillator becomes half in 5 minutes. The amplitude after next 10 minutes will be |
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Answer» A |
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| 17. |
Consider an atom with atomic number Z as consisting of a positive point charge at the centre and surrounded by a distribution of negative electricity uniformly distributed within a sphere of radius R. The electric field at a point inside the atom at a distance r from the centre is |
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Answer» `(ZE)/(4pi epsilon_(0))[(1)/(r^(2))-( r )/(R^(3))]` |
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| 18. |
Assertion. A sphrical equipotential surface is not possible for a pointcharge. Reason. A spherical equipotential surface is possible inside a spherical capacitor. |
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Answer» both, ASSERTION and REASON are true and the Reason is correctexplanation of the Assertion. |
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| 19. |
Which of the following is quantized according to Bohr's theory of hydrogen atom? |
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Answer» ACCELERATION of electron |
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| 20. |
No. of waves of a certain colour light are 2000 in 1 mm distance in air, then what will be wavelength of light in medium of refractive Index 1.25 ? |
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Answer» 1000 Å `:.lambda_("MEDIUM")=(lambda_("air"))/(MU)=(5000Å)/(1.25)=4000Å` |
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| 21. |
(A): Davisson - Germer experiment established the wave nature of electrons. (R): If electrons have wave nature, they can interfere and show diffraction. |
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Answer» A and R are TRUE and R is the CORRECT explanation of A. |
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| 22. |
The radius of earth is 6400 km and that of mars is 3200 km the mass of earth is 10 times the mass of mars. An object weights 200 N on the surface of earth. Its weight on the surface of Mars is : |
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Answer» 8 N |
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| 23. |
If an object is placed at 10 cminfront of a concave mirror of focal length 15 cm. The magnification of image is |
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Answer» `- 1.5` |
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| 24. |
In the middle of the depletion layer of reverse biased p-n junction, the |
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Answer» electric field is zero |
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| 25. |
Three identical specimens of magnetic maerials , uniform magnetic field. Draw the modification in the field lines in each case. Justify your answer. |
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Answer» Solution :We know that nickel is ferromagnetic , ANTIMONY is diamagnetic and aluminium is paramagnetic in nature. Modified field lines in specimens of these materials have been shown in ADJOINING fig. Since RELATIVE permeability of a ferromagnetic material is very high `(mu_r gt gt 1)` , hence all the field lines bend and pass through the ferromagnetic material. As relative permeability of a paramagnetic material is SLIGHTLY more than `1 (mu_r gt 1)` , magnetic field lines slightly bends towards the paramagnetic materials. As relative permeability of a diamagnetic material is slightly less than `1(mu_r lt1)` , magnetic field lines bend away from the diamagnetic material. 
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| 26. |
When are two identical waves said to interfere (a) constructively (b) destructively? |
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Answer» Solution :(a) Two identical waves when interfere constructively. RESULT in maximum INTENSITY (`I_("max"=4a^2` where 'a' is the amplitude ) (b) Two identical waves when interfere DESTRUCTIVELY, result in a zero or minimum intensity `(I_("max")=0).` |
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| 27. |
If A and B persons are moving with V_(A)and V_(B)velocities in opposite directions. Magnitude of relative velocity of B w.r.t. A is x and magnitude of relative velocity of A w.r.t B is y. Then |
| Answer» ANSWER :B | |
| 28. |
The ratio of accelerations due to gravity g_(1) : g_(2) on the surface of two planets is 5 : 2 and the ratio of their respective average densities rho_(1) : rho_(2) is 2 : 1. What is the ratio of respective escape velocities v_(1) : v_(2) from the surface of the planets ? |
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Answer» `5: 2` `v_(E )=sqrt((2GM)/(R ))=sqrt(2gR)""` ….(i) when g is GRAVITY, R is the radius of the planet, G is the gravitational constant and M is the mass of the planet. As mass`="volume" xx" density or " M=(4)/(3)piR^(3)rho` `:. M_(1)=(4)/(3)piR_(1)^(3)rho_(1)" and " M_(2)=(4)/(3)piR_(2)^(3)rho_(2)` Let `M_(1)` and `M_(2)` be the masses of the planets and `rho_(1)` and `rho_(2)` be the densities of the planets. As we know, `g=(GM)/(R^(2))` `:. (g_(1))/(g_(2))=(M_(1)R_(2)^(2))/(M_(2)R_(1)^(2))=(5)/(2) rArr ((4)/(3)piR_(1)^(3)xxR_(2)^(2)rho_(1))/((4)/(3)piR_(2)^(3)xxR_(1)^(2)rho_(2))=(5)/(2)` `[:. g_(1) : g_(2)=5 : 2]` `" or (R_(1))/(R_(2))=(5)/(2)xx(rho_(2))/(rho_(1))=(5)/(2)xx(1)/(2)=(5)/(4)[`:.` rho_(1) : rho_(2)=2 : 1]` Now, the ratio of respective escape velocities `v_(e_(1)) : v_(e_(2))=sqrt(g_(1)R_(1)):sqrt(g_(2)R_(2))=(5)/(2sqrt(2))""`[Using eqn.(i)] |
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| 29. |
A closely wound solenoid 80 cm long has 5 layers of windings of 400 turns each. The diameter of the solenoid is 1.8 cm. If the current carried is 8.0 A, estimate the magnitude of B inside the solenoid near its centre. |
| Answer» SOLUTION :`8pi XX 10^(-3) T ~~ 2.5 xx 10^(-2) T` | |
| 30. |
A wire carrying 100A is bent into a circular loop of 5cm radius. The flux density at its centre in tesla is |
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Answer» `22.56 XX 10^(-4)` |
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| 31. |
Figure shows an overhead view of two particles moving at constant momentum along horizontal paths. Particle 1, with momentum magnitude p_(1)=5.0kg*m//s, has position vector vecr_(1) and will pass 2.0 m from point O. Particle 2, with momentum magnitude p_(2)=2.0kg*m//s, has position vector vecr_(2) and will pass 4.0 m from point O. What are the magnitude and direction of the net angular momentum vecL about point O of the two particle system? |
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Answer» <P> Solution :To find `vecL`, we can first find the individual angular momenta `vecl_(1)andvecl_(2)` and then add them. To evaluate their magnitudes, we can use any one of EQS. Through. HOWEVER, Eq. is easiest, because we are given the perpendicular distances `r_(bot1)(=2.0m)andr_(BOT2)(=4.0m)` and the momentum magnitudes `p_(1)andp_(2)`.Calculations: For particle 1, Eq. yields `l_(1)=r_(bot1)p_(1)=(2.0)(5.0kg*m//s)` = `10kg*m^(2)//s`. To find the direction of vector `vecl_(1)`, we use Eq. and the right-hand rule for vector products. For `vecr_(1)xxvecp_(1)`, the vector product is out of the page, perpendicular to the plane of Fig. This is the positive direction, consistent with the counterclockwise rotation of the particle.s position vector `vecr_(1)` around O as particle 1 moves. Thus, the angular momentum vector for particle 1 is `l_(1)=+10kg*m^(2)//s`.  Similarly, the magnitude of `vecl_(2)` is `l=r_(bot2)p_(2)=(4.0m)(2.0kg*m//s)` = `8.0kg*m^(2)//s`, and the vector product `vecr_(2)xxvecp_(2)` is into the page, which is the negative direction, consistent with the clockwise rotation momentum vector for particle 2 is `l_(2)=-8.0kg*m^(2)//s` The net angular momentum for the two particle system is `L=l_(1)+l_(2)=+10kg*m^(2)//s+(-8.0kg*m^(2)//s)` = `+2.0kg*m^(2)//s`. |
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| 32. |
An object is there on a wall. Now by help of convex lens, an image of object is obtained of same size as of object on the opposite parallel wall. If the lens is at distance d from second wall, then what should be the focal length of lens ? |
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Answer» `d/4` TAKING |v|=|u|=d u=-d (From SIGN convention) `therefore1/f=1/d=((1)/(-d))` =`1/d+1/d` `therefore1/f=2(1/d) thereforef=d/2` |
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| 33. |
What is the shape of a wavefront when (a) light is emitted by a point source in an isotropic medium. (b) light is emerging from a convex lens when a point source is placed at its focus. (c) light of the sun is reaching the earth. (d) light is diverging from a slit. |
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Answer» |
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| 34. |
Four cells each of emf 2V and internal resistance 1 ohm are connected in parallel with an external resistance of 6 ohm. The current in the external resistance is |
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Answer» 0.32 A |
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| 35. |
The period T of circular motion of a particle of mass m and charge q moving inside a uniform magnetic field of induction B is given by __________ . |
| Answer» Solution :N/A | |
| 36. |
Explain why the reactance offered by a capacitor decreases with increasing frequency of an alternating voltage |
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Answer» SOLUTION :We KNOW that a capacitor does not allow flow of direct current through it because the gap between the two plates of capacitor offers an infinite resistance. When an alternating voltage is applied across a capacitor, the capacitor plates are alternately charged and DISCHARGED. As a result of this changing charge (and hence potential) a current is established through the capacitor. It is therefore clear that a capacitor will pass more current through it if the charge (or voltage) is changing at a faster RATE i.e., the frequency of alternating voltage supply is higher. It means that the reactance offered by a capacitor decreases with increase in frequency of alternating supply. In fact reactance of a capacitor is GIVEN by: `X_( C) = 1/(C omega) = 2piv C`. |
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| 37. |
The graph between deBroglie wavelength (lamda) and (lamdap) is (p is the linear momentum of the particle) |
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Answer»
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| 38. |
An object is kept at a distance of 4 cm form the first focus of a convex lens. A real image is formed ata distance of 9 cm from its second focus. What is the focal length of that lens is___( in cm) |
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| 39. |
जाँच कीजिए की वस्तुओं के निम्नलिखित संग्रह समुच्चय है अथवा नहीं। J अक्षर से शुरू होने वाले वर्ष के सभीदिनों का संग्रह। |
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Answer» समुच्चय होगा |
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| 40. |
What is total internal reflection. Explain the phenomenon using Huygen's principle. |
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Answer» Solution :Total internal reflection: When a light ray travels from denser medium to rarer medium, the angle of incidence is greater than critical angle then it reflects into the same medium. This phenomenon is called total internal reflection. Huygen's principle : According to Huygen's principle, every POINT on the wavefront AB is a source of secondary wavelets and time during which wavelets from B reaches at C. Let `tau` be the time taken by thewave FRONT to advance from B to C. Then distance `BC=upsilon tau` In order to CONSTRUCT reflected WAVELENGTH we draw, a sphere of RADIUS `upsilon tau` from point A. Let CE represent the tangent drawn from C to this sphere. `AE=BC=vtau` Consider the triangles EAC and BAC are congruent. `therefore`Angles i and r would be equal. This is the law of reflection. 
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| 41. |
An iron nail is attracted by a magnet. What is source of kinetic energy ? |
| Answer» Solution :ENERGY is REQUIRED to MAKE a MEGNET. A part of this energy is converted into K.E. | |
| 42. |
An endoscope employed by a physician to view the internal parts of the body is based on the principle of |
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Answer» refraction |
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| 43. |
If the magnetic field is parallel to the positive y-axis and the charged particle is moving along the positive x-axis (figure ), which way would the Lorentz force be for (a) and electron (negative charge), (b) a proton (positive charge) |
Answer» Solution :The velocity v of particle is along the x-axis while B , the magnetic FIELD is along the y-axis, so `v xx B` is along the z-axis (screw RULE or RIGHT -hand thumb rule ) . (a) For electron it will be along -z axis . (b) For a positive charge (PROTON) the force is along +z axis . 
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| 44. |
In a double-slit experiment the angular width of a fringe is found to be 0.2^(0) on a screen placed 1 m away. The wavelenght of light used is 600 nm. What will be the angular width of the fringe if the entire experimental apparatus is immersed in water? Take refractive index of water to be 4"/"3. |
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Answer» SOLUTION :ANGULAR fringe separation, `THETA= (LAMBDA)/(d)" or "d=(lambda)/(theta)""" In water, "d= (lambda.)/(theta.)` `therefore (lambda)/(theta)=(lambda.)/(theta.)" or "(theta.)/(theta)=(lambda.)/(lambda)= (1)/(mu)=(3)/(4)` or `theta.= (3)/(4)theta= (3)/(4)xx 0.2^(0)= 0.15^(0)`. |
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| 45. |
A closed loop moves normal to a constant electric field between the plates of capacitor with plane of loop is normal to the field. When the loop is partially outside the plates of capacitor, the induced current in the loop |
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Answer» DEPENDS on SPEED of loop |
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| 46. |
A : Wires of the transmission lines carrying A.C. are made of multiple stands. R : A.C. flows on surface of the conductor. |
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Answer» If both Assertion & Reason are true and the reason is the CORRECT explanation of the assertion, then MARK (1) |
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| 47. |
Two inductors are connected in parallel to each other and their resultant is found to be 2.4 H. If one of themis having self-inductance of 6 H then what will be selfinductance of the other inductor in henry? |
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Answer» `(L_(1)L_(2))/(L_(1)+L_(2))` `(L_(1)L_(2))/(L_(1)+L_(2))= 2.4` `L_(1)= 6H` `IMPLIES (6L_(2))/(6+L_(2))= 2.4 implies L_(2)= 2.4 +0.4L_(2)implies 0.6 xx L_(2)=2.4` `implies L_(2)=4` |
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| 48. |
Give the magnitude and direction of the net force acting on a) a drop of rain falling down with a constant speed b) a cork of mass 10 g floating on water c) a kite skillfully held stationary in the sky d) a car moving with a constant velocity of 30 km/h on a rough road e) a high-speed electron in space farfrom all material objects, and free of electric and magnetic fields. |
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Answer» Solution : a) As the rain drop is falling with a constant SPEED, its acceleration a = 0. Hence NET force F = ma - 0. b) As the cork is floating on water, its weight is being balanced by the upthrust (equal to weight of water displaced). Hence net force on the cork is zero. c) As the kite is held stationary, net force on the kite is zero, in accordance with Newton.s first law. d) Force is being APPLIED to overcome the force of friction. But as velocity of the car is constant, its acceleration, a = 0. Hence net force on the car F = ma = 0. e) As no field (gravitational / electric / magnetic) is acting on the electron, net force on it is zero. |
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| 49. |
The amplitude of S.H.M. atx=0.05 m is |
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Answer» 0.02 m `=0.02cospi/4=0.02xx(1)/(SQRT2)=0.0141m` |
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