relative<\/sub> = C
\nAnswer:
\n(a) c<\/p>\n<\/p>\n
Question 2.
\nIf the Earth stops rotating about its own axis, g remains unchanged at …………………..
\n(a) Equator
\n(b) Poles
\n(c) Latitude of 45\u00b0
\n(d) No where
\nAnswer:
\n(b) Poles<\/p>\n
Question 3.
\nWhen train stops, the passenger moves forward. It is due to ……………………
\n(a) Inertia of passenger
\n(b) Inertia of train
\n(c) Gravitational pull by Earth
\n(d) None of the above
\nAnswer:
\n(a) Inertia of passenger<\/p>\n
<\/p>\n
Question 4.
\nA particle of mass m moves in the xy plane with a velocity v along the straight line AB. If the angular momention of the particle with respect to origin O is LA<\/sub> when it is at A and LB<\/sub> when it is at B, then …………………….
\n(a) LA<\/sub> = LB<\/sub>
\n(b) LA<\/sub> < LB<\/sub>
\n(c) LA<\/sub> > LB<\/sub>
\n(d) The relationship between LA<\/sub> and LB<\/sub> depends uopn the slope of the line AB<\/p>\n<\/p>\n
Hint:
\nMagnitude of L is, L = mvr sin \u03d5 = mvd
\nd = r sin \u03d5 is the distance of closest approach of the particle so the origin, as \u2018d\u2019 is same for both particles.
\nSo, L A<\/sub> = LB<\/sub>
\nAnswer:
\n(a) LA<\/sub> = LB<\/sub><\/p>\nQuestion 5.
\nA couple produces ……………………….
\n(a) Pure rotation
\n(b) Pure translation
\n(c) Rotation and translation
\n(d) No motion
\nAnswer:
\n(a) Pure rotation<\/p>\n
<\/p>\n
Question 6.
\nA body starting from rest has an acceleration of 20 ms~2 the distance travelled by it in the sixth second is ……………………..
\n(a) 110 m
\n(b) 130m
\n(c) 90m
\n(d) 50 m
\nHint:
\nDistance travelled in nth<\/sup> second, u = 0
\nSn<\/sub> = u + \\(\\frac{1}{2}\\)a(2n – 1)
\nS6<\/sub> = 0 + \\(\\frac{1}{2}\\) \u00d7 20 \u00d7 (2 \u00d7 6 – 1); S6<\/sub> = 110 m
\nAnswer:
\n(a) 110 m<\/p>\nQuestion 7.
\nA lift of mass 1000 kg, which is moving with an acceleration of 1m\/s2<\/sup> in upward direction has tension has developed in its string is ………………………
\n(a) 9800 N
\n(b) 10800 N
\n(c) 11000 N
\n(d) 10000 N
\nHint:
\nTension, T = mg + ma = m(g + a) = 1000 (10 + 1)
\nT = 11000 N
\nAnswer:
\n(c) 11000 N<\/p>\n<\/p>\n
Question 8.
\nThe relation between acceleration and displacement of four particles are given below ………………………..
\n(a) ax<\/sub> = 2x
\n(b) ax<\/sub> = + 2x2<\/sup>
\n(c) ax<\/sub> = -2x2<\/sup>
\n(d) ax<\/sub> = -2x
\nAnswer:
\n(d) ax<\/sub> = -2x<\/p>\nQuestion 9.
\nA sonometer wire is vibrating in the second overtone. In the wire there are, ……………………..
\n(a) Two nodes and two antinodes
\n(b) One node and two antinodes
\n(c) Four nodes and three antinodes
\n(d) Three nodes and three antinodes
\nAnswer:
\n(d) Three nodes and three antinodes<\/p>\n
<\/p>\n
Question 10.
\nWhich of the following is the graph between the light (h) of a projectile and time (t), when it is projected from the ground ………………………..
\n(a)
\n(b)
\n(c)
\n(d)
\nAnswer:
\n(c) <\/p>\n
Question 11.
\nAccording to kinetic theory of gases, the rms velocity of the gas molecules is directly proportional to ………………………
\n(a) \\(\\sqrt{T}\\)
\n(b) T3<\/sup>
\n(c) T
\n(d) T4<\/sup>
\nHint:
\nThe rms velocity, Vrms<\/sub> = \\(\\sqrt{3KT\/m}\\) \u21d2 Vrms<\/sub> \u221d \\(\\sqrt{T}\\)
\nAnswer:
\n(a) \\(\\sqrt{T}\\)<\/p>\nQuestion 12.
\nA body of mass m moving with velocity v collides head on with another body of mass 2m which is initially at rest. The ratio of K.E of colliding body before and after collision will be ……………………..
\n(a) 1 : 1
\n(b) 2 : 1
\n(c) 4 : 1
\n(d) 9 : 1
\nHint:
\nKE of colliding bodies before collision = \\(\\frac{1}{2}\\) mv2<\/sup>
\nAfter collision the mass = m + 2m = 3m
\nvelocity becomes V’ = \\(\\left(\\frac{m_{1}-m_{2}}{m_{1}+m_{2}}\\right)\\)v = \\(\\frac{mv}{3m}\\) = \\(\\frac{v}{3}\\)
\nKE after collision = \\(\\frac{1}{2}\\)m (\\(\\frac{V}{3}\\)2<\/sup> = \\(\\frac{1}{9}\\) (\\(\\frac{1}{2}\\) mv2<\/sup>)
\n\\(\\frac{\\mathrm{KE}_{\\text {before }}}{\\mathrm{KE}_{\\text {after }}}=\\frac{\\frac{1}{2} \\mathrm{mv}^{2}}{\\frac{1}{9}\\left(\\frac{1}{2} \\mathrm{mv}^{2}\\right)}=9: 1\\)
\nAnswer:
\n(d) 9 : 1<\/p>\n<\/p>\n
Question 13.
\nFour particles have velocity 1, 0, 2 and 3ms-1<\/sup>. The root mean square velocity of the particles is ……………………..
\n(a) 3.5 ms-1<\/sup>
\n(b) \\(\\sqrt{3.5}\\) ms-1<\/sup>
\n(c) 1.5ms-1<\/sup>
\n(d) Zero
\nHint:<\/p>\n<\/p>\n
Answer:
\n(b) \\(\\sqrt{3.5}\\) ms-1<\/sup><\/p>\n<\/p>\n
Question 14.
\nTwo vibrating tuning forks produce progressive waves given by y1<\/sub> = 4 sin 500 \u03c0t and y2<\/sub> = 2 sin 506 \u03c0t where t is in seconds Number of beat produced per minute is ………………………
\n(a) 360
\n(b) 180
\n(c) 3
\n(d) 60
\nHint:<\/p>\n
\nf2<\/sub> – f1<\/sub> = 3 = beats per sec and 3 \u00d7 60 = 180 beats per min<\/p>\nAnswer:
\n(b) 180<\/p>\n
Question 15.
\nWorkdone by a simple pendulum in one complete oscillation is …………………………..
\n(a) Zero
\n(b) Jmg
\n(c) mg cos \u03b8
\n(d) mg sin \u03b8
\nAnswer:
\n(a) Zero<\/p>\n
PART – II<\/span><\/p>\nAnswer any six questions in which Q. No 23 is compulsory. [6 \u00d7 2 = 12]<\/span><\/p>\nQuestion 16.
\nA girl is swinging in the sitting position. How will the period of the swing be changed if she stands up?
\nAnswer:
\nThis can be explained using the concept of a simple pendulum. We know that the time period of a simple pendulum is given by
\nT = 2\u03c0\\(\\sqrt{l\/g}\\) i.e; T \u221d\\(\\sqrt{l}\\)
\nWhen the girl stands up, the distance between the point of suspension and the centre of mass of the swinging body decreases i.e., l decreases, so T will also decrease.<\/p>\n
Question 17.
\nA car starts to move from rest with uniform acceleration 10 ms-2<\/sup> then after 2 sec, what is its velocity?
\nAnswer:
\na =10 ms-2<\/sup>;
\nt = 2s;
\nw = 0;
\nv = ?
\nv = u + at
\nv = 0 + 10 \u00d7 2
\n= 20 ms-1<\/sup><\/p>\n<\/p>\n
Question 18.
\nState Lami\u2019s theorem?
\nAnswer:
\nIf a system of three concurrent and coplanar forces is in equilibrium, then Lami\u2019s theorem states that the magnitude of each force of the system is proportional to sine of the angle between the other two forces. The constant of proportionality is same for all three forces.<\/p>\n
Question 19.
\nDue to the action of constant torque, a wheel from rest makes n rotations in t seconds? Show that the angular acceleration of a wheel as \\(\\frac{4 \\pi n}{t^{2}}\\) rad s-2<\/sup>
\nAnswer:
\nInitial angluar velocity \u03c90<\/sub> = 0
\nNumber of rotations in t seconds = n
\nangular displacement \u03b8 = 2\u03c0n
\nbut, \u03b8 = \u03c90<\/sub>t + \\(\\frac{1}{2}\\)\u03b1t2<\/sup>
\n2\u03c0n = \\(\\frac{1}{2}\\)\u03b1t2<\/sup>
\n\u03b1 = \\(\\frac{4 \\pi n}{t^{2}}\\)<\/p>\nQuestion 20.
\nWhy a given sound is louder in a hall than in the open?
\nAnswer:
\nIn a hall, repeated reflections of sound take place from the walls and the ceiling. These reflected sounds mix with original sound which results in increase the intensity of sound. But in open, no such a repeated reflection is possible. .\u2019. sound will not be louder as in hall.<\/p>\n
<\/p>\n
Question 21.
\nWhat are the differences between connection and conduction?
\nAnswer:
\nConduction:
\nConduction is the process of direct transfer of heat through matter due to temperature difference. When two objects are in direct contact with one another, heat will be transferred from the hotter object to the colder one. The objects which allow heat to travel easily through them are called conductors.<\/p>\n
Convection:
\nConvection is the process in which heat transfer is by actual movement of molecules in fluids such as liquids and gases. In convection, molecules move freely from one place to another.<\/p>\n
Question 22.
\nWhy two holes are made to empty an oil tin?
\nAnswer:
\nWhen oil comes out through a tin with one hole, the pressure inside the tin becomes less than the atmospheric pressure, soon the oil stops flowing out. When two holes are made in the tin, air keeps on entering the tin through the other hole and maintains pressure inside.<\/p>\n
<\/p>\n
Question 23.
\nIf the length of the simple pendulum is increased by 44% from its original length, calculate the percentage increase in time period of the pendulum?
\nAnswer:
\nSince T \u221d \\(\\sqrt{l}\\) = Constant \\(\\sqrt{l}\\)<\/p>\n
<\/p>\n
\u2234 Tf<\/sub> = 1.2 Ti<\/sub> = Ti<\/sub> + 20% Ti<\/sub><\/p>\nQuestion 24.
\nWhen do the real gases obey more correctly the gas equation PV = nRT?
\nAnswer:
\nAn ideal gas is one whose molecules have zero volume and no mutual force between them. At low pressure, the volume of a gas is large and so the volume occupied by the molecules is negligible in comparison to the volume of the gas.<\/p>\n
At high temperature, the molecules have large velocities and so the intermolecular force has no influence on their motion. Hence at low pressure and high temperature, the behaviour of real gases approach the ideal gas behaviour.<\/p>\n
PART – III<\/span><\/p>\nAnswer any six questions in which Q.No. 29 is compulsory. [6 \u00d7 3 = 18]<\/span><\/p>\nQuestion 25.
\nA stone is thrown upwards with a speed v from the top of a tower. It reaches the ground with a velocity 3v. What is the height of the tower?
\nAnswer:
\nFrom equation of motion,
\nv’ = u + at ……………….. (1)
\nh = ut + \\(\\frac{1}{2}\\) at2<\/sup>
\nhere, v’ = av; u = v; a = +g
\nUsing equ. (1)
\n3v = v + gt \u21d2 3v – v = gt
\nt = \\(\\frac{2v}{g}\\)<\/p>\nSubstitute ‘t’ value in equ. (2)
\nh = v(\\(\\frac{2v}{g}\\)) + \\(\\frac{1}{2}\\)g(\\(\\frac{2v}{g}\\))2<\/sup> = \\(\\frac { 2v^{ 2 } }{ g } \\) + \\(\\frac{1}{2}\\)g (\\(\\frac{2v}{g}\\))2<\/sup>
\nh = \\(\\frac { 2v^{ 2 } }{ g } \\) + \\(\\frac { 2v^{ 2 } }{ g } \\)
\n= \\(\\frac { 4v^{ 2 } }{ g } \\) g = 10 ms-2<\/sup>
\n= \\(\\frac { 4v^{ 2 } }{ 10 } \\); h = \\(\\frac { 2v^{ 2 } }{ 5 } \\)<\/p>\n<\/p>\n
Question 26.
\nAn object is projected at an angle such that the horizontal range is 4 times of the maximum height. What is the angle of projection of the object?
\nAnswer:
\nGiven:
\nHorizontal range = 4 Hmax<\/sub>
\nHorizontal range = \\(\\frac{u^{2} \\sin 2 \\theta}{g}\\) = \\(\\frac{2 u^{2} \\sin \\theta \\cos \\theta}{g}\\)
\nMaximum height = \\(\\frac{u^{2} \\sin ^{2} \\theta}{2 g}\\)
\nas given, \\(\\frac{2 u^{2} \\sin \\theta \\cos \\theta}{g}\\) = \\(\\frac{4 u^{2} \\sin ^{2} \\theta}{2 g}\\)
\n2 cos \u03b8 = 2 sin \u03b8
\ntan \u03b8 = 1
\n\u2234 \u03b8 = 45\u00b0<\/p>\nQuestion 27.
\nA room contains oxygen and hydrogen molecules in the ratio 3 : 1. The temperature of the room is 27\u00b0C. The molar mass of 02<\/sub> is 32 g mol-1<\/sup> and for H2<\/sub>, 2 g mol-1<\/sup>. The value of gas constant R is 8.32 J mol-1<\/sup>1 k-1<\/sup>. Calculate rms speed of oxygen and hydrogen molecule?
\nAnswer:
\n(a) Absolute Temperature T = 27\u00b0C = 27 + 273 = 300 K.
\nGas constant R = 8.32 J mol-1<\/sup> K-1<\/sup>
\nFor Oxygen molecule: Molar mass<\/p>\nM = 32 gm\/mol = 32 \u00d7 10-3<\/sup> kg mol-1<\/sup>
\nrms speed vrms<\/sub> = \\(\\sqrt { \\frac { 3RT }{ M } } \\) = \\(\\sqrt{\\frac{3 \\times 8.32 \\times 300}{32 \\times 10^{-3}}}\\) = 483.73 ms-1<\/sup> ~ 484ms-1<\/sup><\/p>\nFor Hydrogen molecule: Molar mass M = 2 \u00d7 10-3<\/sup> kg mol-1<\/sup>
\nrms speed vrms<\/sub> = \\(\\sqrt { \\frac { 3RT }{ M } } \\) = \\(\\sqrt{\\frac{3 \\times 8.32 \\times 300}{2 \\times 10^{-3}}}\\) = 1934 ms-1<\/sup> = 1.93 K ms-1<\/sup><\/p>\nNote that the rms speed is inversely proportional to \\(\\sqrt{M}\\) and the molar mass of oxygen is 16 times higher than molar mass of hydrogen. It implies that the rms speed of hydrogen is 4 times greater than rms speed of oxygen at the same temperature. \\(\\frac{1934}{484}\\) ~ 4.<\/p>\n
<\/p>\n
Question 28.
\nExplain about an angle of friction?
\nAnswer:
\nThe angle of friction is defined as the angle between the normal force (N) and the resultant force (R) of normal force and maximum friction force (\\(f_{s}^{\\max }\\))<\/p>\n
<\/p>\n
In the figure the resultant force is R = \\(\\sqrt{\\left(f_{s}^{\\max }\\right)^{2}+\\mathrm{N}^{2}}\\)
\ntan \u03b8 = \\(\\frac{f_{s}^{\\max }}{\\mathrm{N}}\\) ………………….. (1)<\/p>\n
But from the frictional relation, the object begins to slide when \\(f_{s}^{\\max }=\\mu_{\\mathrm{s}} \\mathrm{N}\\)
\nor when \\(\\frac{f_{s}^{\\max }}{\\mathrm{N}}\\) = \u00b5s<\/sub> ………………….. (2)<\/p>\nFrom equations (1) and (2) the coefficient of static friction is
\n\u00b5s<\/sub> = tan \u03b8 ……………………. (3)
\nThe coefficient of static friction is equal to tangent of the angle of friction.<\/p>\n<\/p>\n
Question 29.
\nHow does resolve a vector into its component? Explain?
\nAnswer:
\ncomponent of a resolve:
\nIn the Cartesian coordinate system any vector \\(\\vec { A } \\) can be resolved into three components along x, y and z directions. This is shown in figure. Consider a 3-dimensional coordinate system. With respect to this a vector can be written in component form as
\n\\(\\vec { A } \\) = Ax<\/sub> \\(\\hat { i } \\) + Ay<\/sub>\\(\\hat { j } \\) + Az<\/sub>\\(\\hat { k } \\)
\nComponents of a vector in 2 dimensions and 3 dimensions<\/p>\n<\/p>\n
<\/p>\n
Here Ax is the x-component of \\(\\vec { A } \\), Ay is the y-component of \\(\\vec { A } \\) and Az<\/sub> is the z component of \\(\\vec { A } \\).
\nIn a 2-dimensional Cartesian coordinate system (which is shown in the figure) the vector \\(\\vec { A } \\) is given by
\n\\(\\vec { A } \\) = Ax<\/sub> \\(\\hat { i } \\) + Ay<\/sub> \\(\\hat { j } \\)<\/p>\nIf \\(\\vec { A } \\) makes an angle \u03b8 with x axis, and Ax<\/sub> and Ay<\/sub> are the components of A along x-axis and y-axis respectively, then as shown in figure,
\nAx<\/sub> \u03b8 = A cos \u03b8, A = A sin \u03b8
\nwhere \u2018A\u2019 is the magnitude (length) of the vector \\(\\vec { A } \\), A = \\(\\sqrt{\\mathrm{A}_{x}^{2}+\\mathrm{A}_{y}^{2}}\\)<\/p>\n<\/p>\n
Question 30.
\nDerive an expression for energy of an orbiting satellite?
\nAnswer:
\nThe total energy of the satellite is the sum of its kinetic energy and the gravitational potential energy. The potential energy of the satellite is,
\nU = \\(-\\frac{\\mathrm{GM}_{s} \\mathrm{M}_{\\mathrm{E}}}{\\left(\\mathrm{R}_{\\mathrm{E}}+h\\right)}\\) ………………….. (1)<\/p>\n
Here Ms<\/sub> -mass of the satellite, ME<\/sub> -mass of the Earth, RE<\/sub> – radius of the Earth.
\nThe Kinetic energy of the satellite is
\nK.E = \\(\\frac{1}{2}\\) Ms<\/sub>v2<\/sup> ………………….. (2)<\/p>\nHere v is the orbital speed of the satellite and is equal to
\nv = \\(\\sqrt{\\frac{\\mathrm{GM}_{\\mathrm{E}}}{\\left(\\mathrm{R}_{\\mathrm{E}}+h\\right)}}\\)<\/p>\n
Substituting the value of v in (2) the kinetic energy of the satellite becomes,
\nK.E = \\(\\frac{1}{2} \\frac{\\mathrm{GM}_{\\mathrm{E}} \\mathrm{M}_{s}}{\\left(\\mathrm{R}_{\\mathrm{E}}+h\\right)}\\)<\/p>\n
Therefore the total energy of the satellite is
\nE = \\(\\frac{1}{2}\\) \\(\\frac{\\mathrm{GM}_{\\mathrm{E}} \\mathrm{M}_{s}}{\\left(\\mathrm{R}_{\\mathrm{E}}+h\\right)}-\\frac{\\mathrm{GM}_{s} \\mathrm{M}_{\\mathrm{E}}}{\\left(\\mathrm{R}_{\\mathrm{E}}+h\\right)}\\)
\nE = \\(-\\frac{\\mathrm{GM}_{s} \\mathrm{M}_{\\mathrm{E}}}{\\left(\\mathrm{R}_{\\mathrm{E}}+h\\right)}\\)
\nThe total energy implies that the satellite is bound to the Earth by means of the attractive gravitational force.<\/p>\n
Note:
\nAs h approaches \u221e, the total energy tends to zero. Its physical meaning is that the satellite is completely free from the influence of Earth\u2019s gravity and is not bound to Earth at large distance.<\/p>\n
<\/p>\n
Question 31.
\nExplain in detail Newton\u2019s law of cooling?
\nAnswer:
\nNewton\u2019s law of cooling:
\nNewton\u2019s law of cooling body is directly proportional to the difference in the temperature between that body and its surroundings.
\n\\(\\frac{dQ}{dT}\\) \u221d(T – Ts<\/sub>) …………………. (1)
\nThe negative sign indicates that the quantity of heat lost by liquid goes on decreasing with time. Where,<\/p>\n<\/p>\n
T = Temperature of the object
\nTs<\/sub> = Temperature of the surrounding<\/p>\nFrom the graph in figure it is clear that the rate of cooling is high initially and decreases with falling temperature.<\/p>\n
Let us consider an object of mass m and specific heat capacity s at temperature T. Let Ts<\/sub> be the temperature of the surroundings. If the temperature falls by a small amount dT in time dt, then the amount of heat lost is,
\ndQ = msdT …………………….. (2)<\/p>\nDividing both sides of equation (2) by dt
\n\\(\\frac{dQ}{dT}\\) = \\(\\frac{msdT}{dt}\\) ………………….. (3)<\/p>\n
From Newton’s law of cooling
\n\\(\\frac{dQ}{dT}\\) \u221d(T – Ts<\/sub>)
\n\\(\\frac{dQ}{dT}\\) = -a(T – Ts<\/sub>) ………………………… (4)<\/p>\nWhere a is some positive constant.
\nFrom equation (3) and (4)
\n-a (T – Ts<\/sub>) = ms\\(\\frac{dT}{dt}\\)
\n\\(\\frac{d \\mathrm{T}}{\\mathrm{T}-\\mathrm{T}_{s}}\\) = -a\\(\\frac{a}{ms}\\) dt …………………… (5)<\/p>\nIntegrating equation (5) on both sides,<\/p>\n
<\/p>\n
Where b1<\/sub> is the constant of integration. Taking exponential both sides we get,
\nT = Ts<\/sub> + \\(b_{2} e^{\\frac{-a}{m s} t}\\) …………………….. (6)
\nHere b2<\/sub> = eb1<\/sup> Constant<\/p>\n<\/p>\n
Question 32.
\nExplain Laplace\u2019s correction?
\nAnswer:
\nLaplace\u2019s correction: In 1816, Laplace satisfactorily corrected this discrepancy by assuming that when the sound propagates through a medium, the particles oscillate very rapidly such that the compression and rarefaction occur very fast.<\/p>\n
Hence the exchange of heat produced due to compression and cooling effect due to rarefaction do not take place, because, air (medium) is a bad conductor of heat. Since, temperature is no longer considered as a constant here, sound propagation is an adiabatic process. By adiabatic considerations, the gas obeys Poisson\u2019s law (not Boyle\u2019s law as Newton assumed), which is
\nPV\u03b3<\/sup> = Constant …………………. (1)
\nwhere, \u03b3 = \\(\\frac { C_{ p } }{ C_{ v } } \\) which is the ratio between specific heat at constant pressure and specific heat at constant volume. Differentiating equation (1) on both the sides, we get
\n\\(V^{ \\gamma }dP+P(\\gamma ^{ V\\gamma -1 }dV)=0\\)<\/p>\nor<\/p>\n
\\(\\gamma \\mathrm{P}=-\\mathrm{V} \\frac{d p}{d \\mathrm{V}}=\\mathrm{B}_{\\mathrm{A}}\\) ………………….. (2)
\nwhere, BA<\/sub> is the adiabatic bulk modulus of air. Now, substituting equation (2) in equation
\nV = \\(\\sqrt{\\frac{B}{\\rho}}\\), the speed of sound in air is
\nvA<\/sub> = \\(\\sqrt{\\frac{\\mathrm{B}_{\\mathrm{A}}}{\\rho}}=\\sqrt{\\frac{\\gamma \\mathrm{P}}{\\rho}}=\\sqrt{\\gamma v_{\\mathrm{T}}}\\)
\nSince air contains mainly, nitrogen, oxygen, hydrogen etc, (diatomic gas), we take \u03b3 = 1.47. Hence, speed of sound in air is vA<\/sub> = (\\(\\sqrt{1.4}\\)) (280 m s-1<\/sup>) = 331.30 ms-1<\/sup>, which is very much closer to experimental data.<\/p>\n<\/p>\n
Question 33.
\nExplain types of equilibrium?
\nAnswer:
\n<\/p>\n
PART – IV<\/span><\/p>\nAnswer all the questions. [5 \u00d7 5 = 25]<\/span><\/p>\nQuestion 34 (a).
\nWhat are the applications of dimensional analysis?
\nVerify s = ut + \\(\\frac{1}{2}\\)at2<\/sup> by dimensional analysis?
\nAnswer:<\/p>\n<\/p>\n
Given equation is dimensionally correct as the dimensions on the both side are same. Applications of dimensional analysis<\/p>\n
\n- Convert a physical quantity from one system of units to another.<\/li>\n
- Check the dimensional correctness of a given physical equation.<\/li>\n
- Establish relations among various physical quantities.<\/li>\n<\/ol>\n
[OR]<\/p>\n
(b) Explain the types of equilibrium with suitable examples?
\nAnswer:
\nTranslational motion – A book resting on a table.
\nRotational equilibrium – A body moves in a circular path with constant velocity.
\nStatic equilibrium – A wall-hanging, hanging on the wall.
\nDynamic equilibrium – A ball decends down in a fluid with its terminal velocity.
\nStable equilibrium – A table on the floor A pencil
\nUnstable equilibrium – standing on its tip.
\nNeutral equilibrium – A dice rolling on a game board.<\/p>\n
<\/p>\n
Question 35 (a)
\nExplain the motion of block connected by a string in vertical motion?
\nAnswer:
\nWhen objects are connected by strings and a force F is applied either vertically or horizontally or along an inclined plane, it produces a tension T in the string, which affects the acceleration to an extent. Let us discuss various cases for the same.<\/p>\n
<\/p>\n
Vertical motion:
\nConsider two blocks of masses m1<\/sub> and m2<\/sub> (m1<\/sub> > m2<\/sub>) connected by a light and inextensible string that passes over a pulley as shown in Figure 1.<\/p>\nLet the tension in the string be T and acceleration a.<\/p>\n
When the system is released, both the blocks start, Two blocks connected by a string moving, m2<\/sub> vertically upward and m1<\/sub> downward with same acceleration a. The gravitational force m1<\/sub>g on mass m1<\/sub> is used in lifting the mass m2<\/sub>.<\/p>\nThe upward direction is chosen as y direction. The free body diagrams of both masses are shown in Figure 2.<\/p>\n
<\/p>\n
Applying Newton\u2019s second law for mass m2<\/sub>
\nT\\(\\hat { j } \\) – m2<\/sub>\\(\\hat { j } \\)g = m2<\/sub> a\\(\\hat { j } \\)<\/p>\nThe left hand side of the above equation is the total force that acts on m2<\/sub> and the right hand side is the product of mass and acceleration of m2<\/sub> in direction.<\/p>\nBy comparing the components on both sides, we get
\nT -m2<\/sub>g = m2<\/sub>a ……………………. (1)<\/p>\nSimilarly, applying Newton’s law second law of for mass m1<\/sub>
\nT\\(\\hat { j } \\) – m1<\/sub>g\\(\\hat { j } \\) = -m1<\/sub>a\\(\\hat { j } \\)<\/p>\nAs mass m1<\/sub> moves downward (-\\(\\hat { j } \\)), its accleration is along (-\\(\\hat { j } \\))
\nBy comparing the components on both sides, we get
\nT – m1<\/sub>g = -m1<\/sub>a
\nm1<\/sub>g – T = m1<\/sub>a …………………….. (2)<\/p>\nAdding equations (1) and (2), we get
\nm1<\/sub>g – m2<\/sub>g = m1<\/sub>a + m2<\/sub>a
\n(m1<\/sub>g – m2<\/sub>)g = (m1<\/sub> + m2<\/sub>)a …………………….. (3)<\/p>\nFrom equation (3), the acceleration of both the masses is
\na = \\(\\left(\\frac{m_{1}-m_{2}}{m_{1}+m_{2}}\\right)\\)g ……………………… (4)<\/p>\n
If both the masses are equal (m1<\/sub> = m2<\/sub>), from equation (4)
\na = 0<\/p>\nThis shows that if the masses are equal, there is no acceleration and the system as a whole will be at rest. To find the tension acting on the string, substitute the acceleration from the equation (4)
\nT – m2<\/sub>g = m2<\/sub> \\(\\left(\\frac{m_{1}-m_{2}}{m_{1}+m_{2}}\\right)\\)g
\nT = m2<\/sub>g + m2<\/sub>\\(\\left(\\frac{m_{1}-m_{2}}{m_{1}+m_{2}}\\right)\\)g ……………………… (5)
\nBy taking m2<\/sub>g common in the RHS of equation (5)<\/p>\n<\/p>\n
Equation (4) gives only magnitude of accleration.<\/p>\n
For mass m1<\/sub> g the accleration vector is given by \\(\\vec{a}=-\\left(\\frac{m_{1}-m_{2}}{m_{1}+m_{2}}\\right) g \\hat{j}\\)
\nFor mass m2<\/sub> g the accleration vector is given by \\(\\vec{a}=-\\left(\\frac{m_{1}-m_{2}}{m_{1}+m_{2}}\\right) g \\hat{j}\\)<\/p>\n[OR]<\/p>\n
(b) Derive the kinematic equation of motion for constant acceleration?
\nAnswer:
\nConsider an object moving in a straight line with uniform or constant acceleration \u2018a\u2019. Let u be the velocity of the object at time t = 0, and v be velocity of the body at a later time t.<\/p>\n
Velocity – time relation:<\/p>\n
(I) The acceleration of the body at any instant is given by the first derivative of the velocity with respect to time,
\na = \\(\\frac{dv}{dt}\\) or dv = a dt
\nIntegrating both sides with the condition that as time changes from 0 to t, the velocity changes from u to v. For the constant acceleration,<\/p>\n
<\/p>\n
Displacement – time relation:<\/p>\n
(II) The velocity of the body is given by the first derivative of the displacement with respect to time.
\nv = \\(\\frac{ds}{dt}\\) or ds = vdt
\nand since v = u + at,
\nWe get ds = (u + at)dt
\nAssume that initially at time t = 0, the particle started from the origin. At a later time t, the particle displacement is s. Further assuming that acceleration is time-independent, we have
\n\\(\\int_{0}^{s} d s=\\int_{0}^{t} u d t+\\int_{0}^{t} a t d t \\text { or } s=u t+\\frac{1}{2} a t^{2}\\) ……………………. (2)
\nVelocity – displacement relation<\/p>\n
(III) The acceleration is given by the first derivative of velocity with respect to time.
\na = \\(\\frac{dv}{dt}\\) = \\(\\frac{dv}{ds}\\) \\(\\frac{ds}{dt}\\) = \\(\\frac{dv}{ds}\\) v [since ds\/dt = v] where s is displacement traversed.
\nThis is rewritten as a = \\(\\frac{1}{2}\\) \\(\\frac { dv^{ 2 } }{ s } \\) or ds = \\(\\frac{1}{2a}\\) d(v2<\/sup>)
\nIntegrating the above equation, using the fact when the velocity changes from u2<\/sup> to v2<\/sup>, displacement changes from u2<\/sup> to v2<\/sup>, we get<\/p>\n<\/p>\n
We can also derive the displacement s in terms of initial velocity u and final velocity v.
\nFrom equation we can write,
\nat = v – u
\nSubstitute this in equation, we get
\ns = ut + \\(\\frac{1}{2}\\) (v -u)t
\ns = \\(\\frac{(u+v)t}{2}\\)<\/p>\n
<\/p>\n
Question 36 (a).
\nState and prove perpendicular axis theorem?
\nAnswer:
\nPerpendicular axis theorem: This perpendicular axis theorem holds good only for plane laminar objects.<\/p>\n
The theorem states that the moment of inertia of a plane laminar body about an axis perpendicular to its plane is equal to the sum of moments of inertia about two perpendicular axes lying in the plane of the body such that all the three axes are mutually perpendicular and have a common point.<\/p>\n
Let the X and Y-axes lie in the plane and Z-axis perpendicular to the plane of the laminar object. If the moments of inertia of the body about X and Y-axes are Ix and IY respectively and Iz is the moment of inertia about Z-axis, then the perpendicular axis theorem could be expressed as,
\nIz<\/sub> = Ix<\/sub> + Iy<\/sub><\/p>\n