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Physics Test - 37

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Physics Test - 37
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  • Question 1
    1 / -0

    Directions: Read the following passage and answer the question.

    Two charges, each equal to \(q\), are kept at \(x = – a\) and \(x = a\) on the x-axis. A particle of mass m and charge \(q_0 = q/2\) is placed at the origin.

    If charge \(q_0\) is given a small displacement \(y (<< a)\) along the y-axis, the net force acting on the particle is proportional to

    Solution

    Referring to the figure, suppose the charge \(\mathrm{q}_{0}=\mathrm{q} / 2 \) is given a small displacement \(\mathrm{OC}=\mathrm{y}\) along the \(\mathrm{y}\) -axis. The force of repulsion on charge \(\bar{q}_0\) due to the charge \(q_{1}=q\) is,

    \(F_{1}=k \frac{9 q_{0}}{(A C)^{2}}=k \frac{q^{x} q / 2}{\left(a^{2}+y^{2}\right)}\)

    The force of repulsion on charge \(\mathrm{q}_{0}\) due to charge \(\mathrm{q}_{2}=\mathrm{q}\) is,

    \(\mathrm{F}_{2}=\mathrm{k} \frac{\mathrm{q} \mathfrak{q}}{(\mathrm{BC})^{2}}=\mathrm{k} \frac{\mathrm{q}^{\mathrm{x}} \mathrm{q} / 2}{\left(\mathrm{a}^{2}+\mathrm{y}^{2}\right)}\)

    The directions of \(F_{1}\) and \(F_{2}\) are shown in the figure. Force \(F_{1}\) can be resolved into two components \(\left(F_{1}\right) x=F_{1} \sin \theta\) along positive x -direction and \(\left(\mathrm{F}_{1}\right) \mathrm{y}=\mathrm{F}_{1}\) cos \(\theta\) along positive y direction. Similarly, force \(\mathrm{F}_{2}\) can be resolved into two components \(\left(F_{2}\right)_{\mathrm{x}}=\mathrm{F}_{2} \sin \theta\) along negative \(\mathrm{x}\) -direction and \(\left(\mathrm{F}_{2}\right) \mathrm{y}=\mathrm{F}_{2} \cos \theta\) along positive y -direction. since \(\mathrm{F}_{1}=\mathrm{F}_{2}\) components \(\left(\mathrm{F}_{1}\right) \mathrm{x}\) and \(\left(\mathrm{F}_{2}\right) \mathrm{x}\) are equal and opposite and hence, they cancel each other. The net force on charge \(\mathrm{q}_{0}\) is along positive y -direction and is given by;

     

    \(\mathrm{F}=\left(\mathrm{F}_{1}\right)_{\mathrm{y}}+\left(\mathrm{F}_{2}\right)_{\mathrm{y}}=\mathrm{F}_{1} \cos \theta+\mathrm{F}_{2} \cos \theta\)
    Or
    \(F=k \cdot \frac{q^{2}}{\left(a^{2}+y^{2}\right)} \cos \theta\)
    Now \(\cos \theta=\frac{o C}{A C}=\frac{y}{\left(a^{2}+y^{2}\right)^{1 / 2}} .\) 
    Therefore, \(F=k \cdot \frac{q^{2} y}{\left(a^{2}+y^{2}\right)^{3 / 2}}\) along positive \(y\) direction since\((y<
    \(F=k \cdot \frac{q^{2} y}{a^{3}}\)
    So,
    \(F \propto y\)
  • Question 2
    1 / -0

    Two particles execute SHM of the same amplitude and frequency along the same straight line. If they pass one another when going in opposite directions, each time their displacement is half their amplitude, the phase difference between them is:

    Solution

    We know that:The equation for SHM is:

    \(\mathrm{y}=\operatorname{Asin}(\omega+\phi)\)

    As the displacement is half of the amplitudes so:\(\left(\mathrm{y}=\frac{\mathrm{A}}{2}\right)\)

    or \(\frac{\mathrm{A}}{2}=\mathrm{A} \sin (\omega \mathrm{t}+\)\(\phi) \)

    \((\omega t+\phi)=\frac{1}{2} \)

    \(\therefore \omega \mathrm{t}+\phi=30^{\circ} \text { or } 150^{\circ}\)

    Since the two particles are going in opposite directions, the phase of one is \(30^{\circ}\) and that of the other \(150^{\circ} .\)

    So the phase difference between the two particles:

    \(=150^{\circ}-30^{\circ}\)

    \(=120^{\circ}\)

    \(=\frac{2 \pi}{3}\)

  • Question 3
    1 / -0

    The electric field at a point is:

    Solution

    The electric field at a point is continuous if there is no charge at that point and discontinuous if there is a charge at that point.

    Electric field is a region of space in which an electric charge experiences a force. The direction of the electric field at a point in space is the direction in which a positive test charge moves if placed at that point.

    The electric field at a point is continuous only when there is no negative or positive charge in its vicinity that affects its pathway. If there is no other charge in the medium, The electric field because of any charge will be continuous. It will be discontinuous if there is a charge at that viable point.

    Charged particles tend to change the emergence and divergence of continuous electric field lines.

  • Question 4
    1 / -0

    Compute the fractional change in volume of a glass slab, when subjected to a hydraulic pressure of \(10\) atm. Bulk modulus of glass \(37\) GPA.

    Solution

    Hydraulic pressure exerted on glass slab, \(P\) \(=10\) atm Bulk modulus of glass, \({B}=37 \times 10^{9} ~\mathrm{Nm}^{-2}\)

    Bulk modulus, \(\mathrm{B}= \frac{P}{\frac{\Delta {V}} {V}}\)

    where, \(\frac{\Delta {V}} {V}=\) Fractional change in volume \(\frac{\Delta {V}} {V}=\frac{P} {B}\)

    \(=\frac{10 \times 1.013 \times 10^{5}}{ (37 \times 10^{9})}\)

    \(=2.73 \times 10^{-5}\)

    Therefore, the fractional change in the volume of the glass slab is \(2.73 \times 10^{-5}\).

  • Question 5
    1 / -0

    The rms value of an ac current of \(50 \mathrm{~Hz}\) is \(10 \mathrm{amp} .\) The time taken by the alternating current in reaching from zero to maximum value and the peak value of current will be:

    Solution

    \(\mathrm{I}=10 \mathrm{~A}\)

    \(\mathrm{f}=50 \mathrm{~Hz}\)

    \(\mathrm{I}_{\mathrm{rms}}=\left(\frac{\mathrm{I}_{\mathrm{m}}}{\sqrt{2}}\right)\)

    where \(I_{m}\) is peak value \(I_{m}=\sqrt{2} \cdot I_{\text {rms }}\)

    \(\therefore I_{m}=10 \sqrt{2} A=10 \times 1.41=14.1 \mathrm{~A}\)

    Time taken to reach form \(\mathrm{0}\) to \(\mathrm{I}_{\mathrm{m}}\) is \([(\frac{\mathrm{T}} { 4})-0]=(\frac{\mathrm{T}}{4})\)

    \(\mathrm{t=(\frac{T}{ 4})=(\frac{1} { 4 f})}\)

    \(\therefore \mathrm{t}=[\frac{1}{ \{4 \times 50}\}]=[\frac{1} { 200}] \mathrm{sec}\)

    \(\therefore \mathrm{t}=0.5 \times 10^{-2} \mathrm{sec}\)

    \(\mathrm{t}=5 \times 10^{-3} \mathrm{sec}\)

  • Question 6
    1 / -0

    Find the ratio of the magnitude of linear momentum, if two bodies A and B of mass 9 kg and 25 kg respectively are moving with equal kinetic energy.

    Solution

    Given,

    \(m _{ A }=9 \) kg

    \(m _{ B }=25\) kg

    \(KE _{ A }= KE _{ B }\)

    As we know,

    The relation between the kinetic energy and the momentum is given as,

    \( P ^{2}=2 mKE\)

    Momentum for body A, \((P_{A})^{2}=2 m_{A} \times K E_{A}^{2}\)

    \(\therefore (P_{A})^{2}=2 \times 9 \times K E\)

    \(\Rightarrow (P_{A})^{2}=18 \times K E\)...(1)

    Momentum for body B \((P_{B})^{2}=2 m_{B} \times K E_{B}^{2}\)

    \(\therefore (P_{B})^{2}=2 \times 25 \times K E\)

    \(\Rightarrow (P_{B})^{2}=50 \times K E\)...(2)

    On dividing equation (1) and (2), we get

    \(\frac{(P_{A})^{2}}{(P_{B})^{2}}=\frac{18 \times K E}{50 \times K E}\)

    \(\Rightarrow \frac{(P_{A})^{2}}{(P_{B})^{2}}=\frac{9}{25}\)

    \(\Rightarrow \frac{P_{A}}{P_{B}}=\sqrt{\frac{9}{25}}\)

    \(\Rightarrow \frac{P_{A}}{P_{B}}=\frac{3}{5}\)

    \(\Rightarrow P_{A}: P_{B}=3: 5\)

    So, the ratio of linear momentum is \(3:5\).

  • Question 7
    1 / -0

    In the Young's double slit experiment, the distance between the slits varies in time asd \((\mathrm{t})=\mathrm{d}_0+\mathrm{a}_0 \sin \omega \mathrm{t}\); where \(\mathrm{d}_0\), \(\omega\) and \(\mathrm{a}_0\) are constants. The difference between the largest fringe width and the smallest fringe width obtained over time is given as :

    Solution

    \(\begin{aligned} & \text { Fringe Width, } \beta=\frac{\lambda \mathrm{D}}{\mathrm{d}} \\ & \beta_{\max } \Rightarrow \mathrm{d}_{\min } \text { and } \beta_{\min } \Rightarrow \mathrm{d}_{\max } \\ & \mathrm{d}=\mathrm{d}_0+\mathrm{a}_0 \sin \omega \mathrm{t} \\ & \mathrm{d}_{\max }=\mathrm{d}_0+\mathrm{a}_0 \text { and } \mathrm{d}_{\min }=\mathrm{d}_0-\mathrm{a}_0 \\ & \therefore \beta_{\min }=\frac{\lambda \mathrm{D}}{\mathrm{d}_0+\mathrm{a}_0} \text { and } \therefore \beta_{\max }=\frac{\lambda \mathrm{D}}{\mathrm{d}_0-\mathrm{a}_0} \\ & \beta_{\max }-\beta_{\min }=\frac{\lambda \mathrm{D}}{\mathrm{d}_0-\mathrm{a}_0}-\frac{\lambda \mathrm{D}}{\mathrm{d}_0+\mathrm{a}_0}=\frac{2 \lambda \mathrm{Da}_0}{\mathrm{~d}_0^2-\mathrm{a}_0^2}\end{aligned}\)

  • Question 8
    1 / -0

    A block, released from rest from the top of a smooth inclined plane of inclination 45°, takes t seconds to reach the bottom. The same block, released from rest from the top of a rough inclined plane of the same inclination, takes 2t seconds to reach the bottom. The coefficient of friction is

    Solution
    The acceleration of the block sliding down the smooth inclined plane is \(a_{1}=g \sin \theta\) and down the rough inclined plane is \(a_{2}=g \sin \theta-\mu g \cos \theta .\) Given
    \(t_{1}=t\) and \(t_{2}=2 t .\) If the length of the inclined plane is \(s\), we have or
    \(s =\frac{1}{2} a_{1} t_{1}^{2}=\frac{1}{2} a_{2} t_{2}^{2}\)
    \(a_{1} t_{1}^{2} =a_{2} t_{2}^{2}\)
    or
    \(sin \theta \times t^{2}=(g \sin \theta-\mu g \cos \theta) \times(2 t)^{2}\)
    \(sin \theta=4(\sin \theta-\mu \cos \theta\))
    which gives
    \( \mu=\frac{3}{4}\)
    \( \mu={0.75}\)

  • Question 9
    1 / -0

    The atom bomb is based on the principle of:

    Solution

    The nucleus of a heavy atom (such as uranium, plutonium or thorium), when bombarded with low-energy neutrons, can be split apart into lighter nuclei. This process is called nuclear fission.

    Fission reaction can further be classified into controlled and uncontrolled fission reaction.

    In controlled fission, the chain reaction is controlled and only a controlled amount of reaction is allowed, nuclear reactors in nuclear power plants are one of the examples of the controlled fission reaction.

    And for an uncontrolled fission chain reaction, is allowed to happen unless fission material is over, atomic bomb is one of the examples of an uncontrolled fission reaction.

  • Question 10
    1 / -0

    A rectangular solid box of length 0.3m is held horizontally, with one of its sides on the edge of a platform of height 5m. When released, it slips off the table in a very short time τ=0.01s, remaining essentially horizontal. The angle by which it would rotate when it hits the ground will be (in radians) close to :

    Solution

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