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Physics Test - 16
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Physics Test - 16
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  • Question 1/10
    1 / -0

    A bomber plane is moving horizontally with a speed of 500 m/s and a bomb released from it strikes the ground in 10 seconds. The angle with the horizontal at which the bomb strikes the ground is (g = 10 m/s2)

    Solutions

    Let the vertical component of velocity when the bomb strikes the ground beVv

    Let the horizontal component of velocity when the bomb strikes the ground beVH

    VV=O+gt

    Where t = 10 seconds,VV=10×10=100m/sandVH=500m/s

    tanθ=VVVH=100500=15

    Hence,θ=tan-115

  • Question 2/10
    1 / -0

    When a capillary tube of radius r is immersed in a liquid of density p , the liquid rises to a height h in it. If m is the mass of the liquid in the capillary tube, then the potential energy of this mass of the liquid in the tube is

    Solutions

    As the density of the liquid is constant, whole of the mass of liquid in the capillary is supposed to be concentrated at the h/2. So, the potential energy of the liquid in capillary is,

    V=mgh2

    Or,

    The mass of the liquid in a column between x and x + dx is
    dm=πr2pdx
    Therefore, the potential energy of the liquid in a column of height h is,

    πr2×pgdx=πr2pgxdx

    =πr2pgh22=πr2hpgh/2

    = mgh/2
    Hence the correct choice is (2).

  • Question 3/10
    1 / -0

    If M0 is the mass of an oxygen isotope 8O17, and Mp and Mn are the masses of a proton and a neutron, respectively, then what is the nuclear binding energy of the isotope ?

    Solutions

    Here, Z = 8 and A = 17, therefore,

    B.E. = (8Mp+ (17 - 8)Mn- Mo)c2

    = (8Mp+ 9Mn- Mo)c2

  • Question 4/10
    1 / -0

    A satellite, which is geostationary in a particular orbit, is taken to another orbit. Its distance from the centre of Earth in the new orbit is two times that of the earlier orbit. The time period of the satellite in the second orbit is

    Solutions

    First case
    T2R3
    Second Case
    T22R3

    TT=2R3/2R3/2=23/2

    T=23/2T
    =22×24
    =482hours

  • Question 5/10
    1 / -0

    The separation between plates is reduced by half and the space between them is of dielectric constant 5 and capacitance 8 pF. Calculate the value of capacitance of parallel plate capacitor when reduced by half.

    Solutions

    Capacitance of parallel plate capacitor with air between the plates is C0= Є0A/d.

    When the separation between the plates is reduced to half, C1= Є0A/(d / 2) = 2Є0A/d.

    Thus, final capacitance is C2= 10 x 8 pF = 80 pF.

  • Question 6/10
    1 / -0

    The figure below shows a network of currents, with the magnitudes of currents shown. The current I will be

    Solutions

    According to Kirchoff's law, current entering the circuit is equal to the current leaving the circuit.

    So, 12 + 3 = 18 + I

    Or I = - 3A

  • Question 7/10
    1 / -0

    You are given 48 cells, each of emf 2 V and internal resistance 1Ω . How will you connect them so that the current through an extemal resistance of 3Ω is the maximum?

    Solutions

    Let m cells be connected in series and n such groups be connected in parallel. If the ernf of each cell is E and internal resistance r, then the total ernf of m cells in series is mE and the total internal resistance is mr. When n such groups are in parallel, the effective internal resistance is mr/n. Then, the current through an external resistance R is

    I=mER+mrn=mnEnR+mr

    =mnEnR-mr2+2mnRr

    Now, I will be maximum if the denominator is minimum, i.e. if nR = mr Given R = 3Ωand r = 1Ω
    Using these values, we have 3n = m. But mn = 48
    (given). Therefore,m×n3=48,which m = 12. Thus.

    n= 4. Hence, the correct choice is (2).

  • Question 8/10
    1 / -0

    A capacitor of capacitance 2 μF is charged to a potential difference of 12 V. The charging battery is then removed and the capacitor is connected across an inductor of self-inductance 0.6 mH. The current in the circuit, at a time when the potential difference across the capacitor is 6 V, is

    Solutions

    We know that Q = CV and Q =Qocos wt. Also,
    Qo=CVo.

    coswt=QQo=VVo=612=12orwt=π3.

    Now w is given by

    w=1LC ............(1)

    GivenL=0.6××10-3HandC=2×10-6F.Using these values in Eq. (1) we getw=10523rads-1.

    Now,I=dQdt=ddtQocoswt

    =-Qowsinwt

    I=Qowsinwt=CVowsinwt

    =2×10-6×12×10523sinπ3

    =0.6A

  • Question 9/10
    1 / -0

    A chandelier of mass 550 kg is attached to an aluminium rod with an ultimate stress of 1.1 × 108 N/m2. What should be the cross-sectional area of the rod for the safety factor to be 3? Also, find the strain in the rod? Young&aposs modulus of aluminium = 7 × 1010 N/m2.

    Solutions

  • Question 10/10
    1 / -0

    Monochromatic light is refracted from air into glass of refractive index μ. The ratio of the wavelengths of the incident and refracted waves is

    Solutions

    Since the frequency n of the light does not change as light travels from air into glass, we have,

    va=nλoandVg=nλg

    Thereforeλaλg=VaVg=μ

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