NEET 2017 · Physics

NEET 2017 Physics Questions with Solutions

The NEET 2017 paper had 45 Physics questions from 25 chapters.

Current Electricity had the most questions (4), followed by Gravitation, Ray Optics and Optical Instruments and System of Particles and Rotational Motion with 3 each.

14 questions below have the answer and explanation free; the other 31 are in Premium.

Practise NEET 2017 Physics free

Physics questions: 45
Chapters covered: 25
Solved free here: 14 of 45
Easy / Medium / Hard: 6 / 25 / 14

Difficulty is NEET MIND's own tag for each question.

All 45 NEET 2017 Physics questions

In paper order. Try each one, then open the answer where it is shown.

Question 1 (NEET 2017, Q91)
OscillationsMedium
A spring of force constant $k$ is cut into lengths of ratio $1:2:3$ . They are connected in series and the new force constant is $k'$ . Then they are connected in parallel and force constant is $k''$ . Then $k' : k''$ is
1. Option A: $1 : 14$
2. Option B: $1 : 6$
3. Option C: $1 : 9$
4. Option D: $1 : 11$
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Question 2 (NEET 2017, Q92)
ThermodynamicsHard
Thermodynamic processes are indicated in the following diagram.
1. Option A: P → d, Q → b, R → a, S → c
2. Option B: P → a, Q → c, R → d, S → b
3. Option C: P → c, Q → a, R → d, S → b
4. Option D: P → c, Q → d, R → b, S → a
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Question 3 (NEET 2017, Q93)
Electrostatic Potential and CapacitanceMedium
A capacitor is charged by a battery. The battery is removed and another identical uncharged capacitor is connected in parallel. The total electrostatic energy of the resulting system
1. Option A: Increases by a factor of $2$
2. Option B: Increases by a factor of $4$
3. Option C: Decreases by a factor of $2$
4. Option D: Remains the same
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Question 4 (NEET 2017, Q94)
Mechanical Properties of FluidsHard
A U-tube with both ends open to the atmosphere, is partially filled with water. Oil, which is immiscible with water, is poured into one side until it stands at a distance of $10\ \text{mm}$ above the water level on the other side. Meanwhile the water rises by $65\ \text{mm}$ from its original level (see diagram). The density of the oil is
1. Option A: $928\ \text{kg m}^{-3}$
2. Option B: $650\ \text{kg m}^{-3}$
3. Option C: $425\ \text{kg m}^{-3}$
4. Option D: $800\ \text{kg m}^{-3}$
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Correct answer: (A) $928\ \text{kg m}^{-3}$
Explanation
Let the density of oil be $\rho_o$ . The oil column height above the oil-water interface is: $65\ \text{mm} + 65\ \text{mm} + 10\ \text{mm} = 140\ \text{mm}$ The difference in water levels is: $65\ \text{mm} + 65\ \text{mm} = 130\ \text{mm}$ Equating pressures at the same horizontal level: $\rho_o g (140) = \rho_w g (130)$ $\rho_o = \frac{130}{140} \times 1000$ $\rho_o \approx 928\ \text{kg m}^{-3}$
Question 5 (NEET 2017, Q95)
Dual Nature of Radiation and MatterHard
The de-Broglie wavelength of a neutron in thermal equilibrium with heavy water at a temperature $T$ Kelvin and mass $m$ , is
1. Option A: $\dfrac{2h}{\sqrt{mkT}}$
2. Option B: $\dfrac{h}{\sqrt{mkT}}$
3. Option C: $\dfrac{h}{\sqrt{3mkT}}$
4. Option D: $\dfrac{2h}{\sqrt{3mkT}}$
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Question 6 (NEET 2017, Q96)
GravitationMedium
The acceleration due to gravity at a height $1\ \text{km}$ above the earth is the same as at a depth $d$ below the surface of earth. Then
1. Option A: $d = 2\ \text{km}$
2. Option B: $d = \dfrac{1}{2}\ \text{km}$
3. Option C: $d = 1\ \text{km}$
4. Option D: $d = \dfrac{3}{2}\ \text{km}$
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Question 7 (NEET 2017, Q97)
Motion in a PlaneMedium
The $x$ and $y$ coordinates of the particle at any time are $x = 5t - 2t^2$ and $y = 10t$ respectively, where $x$ and $y$ are in meters and $t$ in seconds. The acceleration of the particle at $t = 2\ \text{s}$ is
1. Option A: $-8\ \text{m/s}^{2}$
2. Option B: $0$
3. Option C: $5\ \text{m/s}^{2}$
4. Option D: $-4\ \text{m/s}^{2}$
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Correct answer: (D) $-4\ \text{m/s}^{2}$
Explanation
Given: $x = 5t - 2t^2, \qquad y = 10t$ Velocity components are: $v_x = \frac{dx}{dt} = 5 - 4t$ $v_y = \frac{dy}{dt} = 10$ Acceleration components are: $a_x = \frac{dv_x}{dt} = -4$ $a_y = \frac{dv_y}{dt} = 0$ Hence, acceleration of the particle at $t = 2\ \text{s} $is:$ $-4\ \text{m s}^{-2}$ $
Question 8 (NEET 2017, Q98)
Current ElectricityMedium
In a common emitter transistor amplifier the audio signal voltage across the collector is $3\ \text{V}$ . The resistance of collector is $3\ \text{k}\Omega$ . If current gain is $100$ and the base resistance is $2\ \text{k}\Omega$ , the power gain of the amplifier is
1. Option A: $20$ and $2000$
2. Option B: $200$ and $1000$
3. Option C: $15$ and $200$
4. Option D: $150$ and $15000$
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Question 9 (NEET 2017, Q99)
Moving Charges and MagnetismHard
An arrangement of three parallel straight wires placed perpendicular to the plane of paper carrying same current $I$ along the same direction is shown in figure. Magnitude of force per unit length on the middle wire $B$ is given by
1. Option A: Option (1)
2. Option B: Option (2)
3. Option C: Option (3)
4. Option D: Option (4)
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Question 10 (NEET 2017, Q100)
GravitationEasy
Two astronauts are floating in gravitational free space after having lost contact with their spaceship. The two will:
1. Option A: Will become stationary
2. Option B: Keep floating at the same distance between them
3. Option C: Move towards each other
4. Option D: Move away from each other
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Question 11 (NEET 2017, Q101)
ThermodynamicsHard
A Carnot engine having an efficiency of $\dfrac{1}{10}$ as heat engine, is used as a refrigerator. If the work done on the system is $10\ \text{J}$ , the amount of energy absorbed from the reservoir at lower temperature is
1. Option A: $100\ \text{J}$
2. Option B: $1\ \text{J}$
3. Option C: $90\ \text{J}$
4. Option D: $99\ \text{J}$
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Question 12 (NEET 2017, Q102)
Moving Charges and MagnetismHard
A $250$ -turn rectangular coil of length $2.1\ \text{cm}$ and width $1.25\ \text{cm}$ carries a current of $85\ \mu\text{A}$ and is subjected to a magnetic field of $0.85\ \text{T}$ . Work done for rotating the coil by $180^{\circ}$ against the torque is
1. Option A: $1.15\ \mu\text{J}$
2. Option B: $9.1\ \mu\text{J}$
3. Option C: $4.55\ \mu\text{J}$
4. Option D: $2.3\ \mu\text{J}$
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Question 13 (NEET 2017, Q103)
Semiconductor ElectronicsMedium
Which one of the following represents forward bias diode?
1. Option A: Circuit (1)
2. Option B: Circuit (2)
3. Option C: Circuit (3)
4. Option D: Circuit (4)
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Question 14 (NEET 2017, Q104)
AtomsMedium
The ratio of wavelengths of the last line of Balmer series and the last line of Lyman series is
1. Option A: $0.5$
2. Option B: $2$
3. Option C: $1$
4. Option D: $4$
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Correct answer: (D) $4$
Explanation
For the last line of Balmer series: $\frac{1}{\lambda_B} = R\left(\frac{1}{2^2} - \frac{1}{\infty^2}\right)$ $\lambda_B = \frac{4}{R}$ For the last line of Lyman series: $\frac{1}{\lambda_L} = R\left(\frac{1}{1^2} - \frac{1}{\infty^2}\right)$ $\lambda_L = \frac{1}{R}$ Hence, $\frac{\lambda_B}{\lambda_L} = 4$
Question 15 (NEET 2017, Q105)
Current ElectricityHard
Figure shows a circuit contains three identical resistors with resistance $R = 9.0\ \Omega$ each, two identical inductors with inductance $L = 2.0\ \text{mH}$ each, and an ideal battery with $\varepsilon = 18\ \text{V}$ . The current $i$ through the battery just after the switch is closed is
1. Option A: $0\ \text{A}$
2. Option B: $2\ \text{mA}$
3. Option C: $0.2\ \text{A}$
4. Option D: $2\ \text{A}$
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Question 16 (NEET 2017, Q106)
Laws of MotionHard
Two blocks $A$ and $B$ of masses $3m$ and $m$ respectively are connected by a massless and inextensible string. The whole system is suspended by a massless spring as shown in figure. The magnitudes of acceleration of $A$ and $B$ immediately after the string is cut, are respectively
1. Option A: $\dfrac{g}{3},\ \dfrac{g}{3}$
2. Option B: $g,\ \dfrac{g}{3}$
3. Option C: $\dfrac{g}{3},\ g$
4. Option D: $g,\ g$
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Question 17 (NEET 2017, Q107)
Electromagnetic InductionMedium
A long solenoid of diameter $0.1\,\text{m}$ has $2 \times 10^4$ turns per meter. At the centre of the solenoid, a coil of $100$ turns and radius $0.01\,\text{m}$ is placed with its axis coinciding with the solenoid axis. The current in the solenoid decreases uniformly from $4\,\text{A}$ to $0\,\text{A}$ in $0.05\,\text{s}$ . If the resistance of the coil is $10\pi^2\,\Omega$ , then the total charge flowing through the coil during this time is:
1. Option A: $16\pi\,\mu\text{C}$
2. Option B: $32\pi\,\mu\text{C}$
3. Option C: $16\,\mu\text{C}$
4. Option D: $32\,\mu\text{C}$
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Correct answer: (D) $32\,\mu\text{C}$
Explanation
Magnetic field inside the solenoid is: $B = \mu_0 n I$ Magnetic flux linked with the coil: $\Phi = NBA = N(\mu_0 n I)(\pi r^2)$ Total induced charge: $\Delta Q = \frac{N\Delta \Phi}{R}$ Substituting the values: $\Delta Q = \frac{100 \times 4\pi \times 10^{-7} \times 2 \times 10^4 \times 4 \times \pi (0.01)^2}{10\pi^2}$ $\Delta Q = 32\,\mu\text{C}$
Question 18 (NEET 2017, Q108)
Units and MeasurementsHard
A physical quantity having dimensions of length can be formed using the quantities $c$ , $G$ and $\dfrac{e^2}{4\pi\varepsilon_0}$ . Which of the following combinations represents length?
1. Option A: Option 1
2. Option B: Option 2
3. Option C: Option 3
4. Option D: Option 4
The answer and explanation for this question are in NEET MIND Premium.
Question 19 (NEET 2017, Q109)
Electromagnetic WavesEasy
In an electromagnetic wave in free space, the root mean square value of electric field is $E_{\text{rms}} = 6\,\text{V/m}$ . The peak value of magnetic field is:
1. Option A: $4.23 \times 10^{-8}\,\text{T}$
2. Option B: $1.41 \times 10^{-8}\,\text{T}$
3. Option C: $2.83 \times 10^{-8}\,\text{T}$
4. Option D: $0.70 \times 10^{-8}\,\text{T}$
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Question 20 (NEET 2017, Q110)
Current ElectricityEasy
The resistance of a wire is $R\,\Omega$ . If it is melted and stretched to $n$ times its original length, then its new resistance will be:
1. Option A: $\dfrac{R}{n^2}$
2. Option B: $nR$
3. Option C: $\dfrac{R}{n}$
4. Option D: $n^2R$
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Question 21 (NEET 2017, Q111)
Ray Optics and Optical InstrumentsEasy
The ratio of resolving powers of an optical microscope for two wavelengths $\lambda_1 = 4000\,\text{\AA}$ and $\lambda_2 = 6000\,\text{\AA}$ is:
1. Option A: $16:81$
2. Option B: $8:27$
3. Option C: $9:4$
4. Option D: $3:2$
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Question 22 (NEET 2017, Q112)
Ray Optics and Optical InstrumentsMedium
A thin prism having refracting angle $10^\circ$ is made of glass of refractive index $1.42$ . This prism is combined with another thin prism of glass of refractive index $1.7$ . The combination produces dispersion without deviation. The refracting angle of the second prism should be:
1. Option A: $10^\circ$
2. Option B: $4^\circ$
3. Option C: $6^\circ$
4. Option D: $8^\circ$
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Question 23 (NEET 2017, Q113)
Wave OpticsMedium
Two Polaroids $P_1$ and $P_2$ are placed with their transmission axes perpendicular to each other. Unpolarised light of intensity $I_0$ is incident on $P_1$ . A third Polaroid $P_3$ is placed between $P_1$ and $P_2$ such that its axis makes an angle $45^\circ$ with that of $P_1$ . The intensity of transmitted light through $P_2$ is:
1. Option A: $\dfrac{I_0}{16}$
2. Option B: $\dfrac{I_0}{2}$
3. Option C: $\dfrac{I_0}{4}$
4. Option D: $\dfrac{I_0}{8}$
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Correct answer: (D) $\dfrac{I_0}{8}$
Explanation
After passing through the first Polaroid: $I_1 = \frac{I_0}{2}$ Using Malus' law through $P_3 $:$ $I_2 = I_1 \cos^2 45^\circ$ $I_2 = \frac{I_0}{2} \times \frac{1}{2} = \frac{I_0}{4}$ $Again through$ P_2 $:$ $I_3 = I_2 \cos^2 45^\circ$ $I_3 = \frac{I_0}{4} \times \frac{1}{2} = \frac{I_0}{8}$ $
Question 24 (NEET 2017, Q114)
Current ElectricityEasy
A potentiometer is an accurate and versatile device to make electrical measurements of E.M.F. because the method involves:
1. Option A: A combination of cells, galvanometer and resistances
2. Option B: Cells
3. Option C: Potential gradients
4. Option D: A condition of no current flow through the galvanometer
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Question 25 (NEET 2017, Q115)
WavesMedium
The two nearest harmonics of a tube closed at one end and open at the other end are $220\,\text{Hz}$ and $260\,\text{Hz}$ . What is the fundamental frequency of the system?
1. Option A: $40\,\text{Hz}$
2. Option B: $10\,\text{Hz}$
3. Option C: $20\,\text{Hz}$
4. Option D: $30\,\text{Hz}$
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Correct answer: (C) $20\,\text{Hz}$
Explanation
For a pipe closed at one end, only odd harmonics are present. Thus, $\frac{nv}{4l} = 220$ and $\frac{(n+2)v}{4l} = 260$ Subtracting the equations: $\frac{2v}{4l} = 40$ $\frac{v}{4l} = 20\,\text{Hz}$ Hence, the fundamental frequency is: $20\,\text{Hz}$
Question 26 (NEET 2017, Q116)
Ray Optics and Optical InstrumentsMedium
A beam of light from a source $L$ is incident normally on a plane mirror fixed at a distance $x$ from the source. The beam is reflected back as a spot on a scale placed just above the source $L$ . When the mirror is rotated through a small angle $\theta$ , the spot of light is found to move through a distance $y$ on the scale. The angle $\theta$ is given by:
1. Option A: $\dfrac{x}{y}$
2. Option B: $\dfrac{y}{2x}$
3. Option C: $\dfrac{y}{x}$
4. Option D: $\dfrac{x}{2y}$
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Question 27 (NEET 2017, Q117)
Semiconductor ElectronicsMedium
The given electrical network is equivalent to:
1. Option A: NOT gate
2. Option B: AND gate
3. Option C: OR gate
4. Option D: NOR gate
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Question 28 (NEET 2017, Q118)
OscillationsMedium
A particle executes linear simple harmonic motion with amplitude $3\,\text{cm}$ . When the particle is at a distance $2\,\text{cm}$ from the mean position, the magnitude of its velocity is equal to that of its acceleration. The time period of the motion is:
1. Option A: $\dfrac{2\pi}{\sqrt{3}}\,\text{s}$
2. Option B: $\dfrac{\sqrt{5}}{\pi}\,\text{s}$
3. Option C: $\dfrac{\sqrt{5}}{2\pi}\,\text{s}$
4. Option D: $\dfrac{4\pi}{\sqrt{5}}\,\text{s}$
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Question 29 (NEET 2017, Q119)
Motion in a PlaneMedium
Preeti reached the metro station and found that the escalator was not working. She walked up the stationary escalator in time $t_1$ . On another day, if she remains stationary on the moving escalator, then the escalator takes her up in time $t_2$ . The time taken by her to walk up on the moving escalator will be:
1. Option A: $(t_1-t_2)$
2. Option B: $\dfrac{t_1+t_2}{2}$
3. Option C: $\dfrac{t_1t_2}{t_2-t_1}$
4. Option D: $\dfrac{t_1t_2}{t_2+t_1}$
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Correct answer: (D) $\dfrac{t_1t_2}{t_2+t_1}$
Explanation
Let the length of escalator be $d$ . Velocity of Preeti relative to escalator: $v_p = \frac{d}{t_1}$ Velocity of escalator: $v_e = \frac{d}{t_2}$ Net velocity while walking on moving escalator: $v = v_p + v_e$ If time taken is $t $,$ $\frac{d}{t}=\frac{d}{t_1}+\frac{d}{t_2}$ $\frac{1}{t}=\frac{1}{t_1}+\frac{1}{t_2}$ $t=\frac{t_1t_2}{t_1+t_2}$ $
Question 30 (NEET 2017, Q120)
System of Particles and Rotational MotionHard
Two discs of the same moment of inertia rotating about their regular axis passing through the centre and perpendicular to the plane of the disc with angular velocities $\omega_1$ and $\omega_2$ are brought into contact face to face with their axes coinciding. The expression for loss of energy during this process is:
1. Option A: Option 1
2. Option B: Option 2
3. Option C: Option 3
4. Option D: Option 4
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Question 31 (NEET 2017, Q121)
Kinetic TheoryMedium
A gas mixture consists of $2$ moles of $O_2$ and $4$ moles of Ar at temperature $T$ . Neglecting all vibrational modes, the total internal energy of the system is:
1. Option A: $11RT$
2. Option B: $4RT$
3. Option C: $15RT$
4. Option D: $9RT$
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Correct answer: (A) $11RT$
Explanation
For diatomic gas $O_2$ without vibrational modes: $U_{O_2}=n\frac{5}{2}RT$ $U_{O_2}=2\times\frac{5}{2}RT=5RT$ For monoatomic gas Ar: $U_{Ar}=n\frac{3}{2}RT$ $U_{Ar}=4\times\frac{3}{2}RT=6RT$ Total internal energy: $U=5RT+6RT=11RT$
Question 32 (NEET 2017, Q122)
Mechanical Properties of SolidsMedium
The bulk modulus of a spherical object is $B$ . If it is subjected to uniform pressure $p$ , then the fractional decrease in radius is:
1. Option A: $\dfrac{p}{3B}$
2. Option B: $\dfrac{p}{B}$
3. Option C: $\dfrac{B}{3p}$
4. Option D: $\dfrac{3p}{B}$
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Correct answer: (A) $\dfrac{p}{3B}$
Explanation
Bulk modulus is defined as: $B=\frac{p}{\Delta V/V}$ For a sphere: $V=\frac{4}{3}\pi r^3$ Hence, $\frac{\Delta V}{V}=3\frac{\Delta r}{r}$ Therefore, $B=\frac{p}{3\Delta r/r}$ So the fractional decrease in radius is: $\frac{\Delta r}{r}=\frac{p}{3B}$
Question 33 (NEET 2017, Q123)
Laws of MotionEasy
One end of a string of length $l$ is connected to a particle of mass $m$ and the other end is connected to a small peg on a smooth horizontal table. If the particle moves in a circle with speed $v$ , the net force on the particle directed towards the centre will be ( $T$ represents the tension in the string):
1. Option A: Zero
2. Option B: $T$
3. Option C: $T + \dfrac{mv^2}{l}$
4. Option D: $T - \dfrac{mv^2}{l}$
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Question 34 (NEET 2017, Q124)
System of Particles and Rotational MotionMedium
A rope is wound around a hollow cylinder of mass $3\,\text{kg}$ and radius $40\,\text{cm}$ . What is the angular acceleration of the cylinder if the rope is pulled with a force of $30\,\text{N}$ ?
1. Option A: $5\,\text{m/s}^2$
2. Option B: $25\,\text{m/s}^2$
3. Option C: $0.25\,\text{rad/s}^2$
4. Option D: $25\,\text{rad/s}^2$
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Question 35 (NEET 2017, Q125)
Wave OpticsHard
Young's double slit experiment is first performed in air and then repeated in a medium other than air. It is found that the eighth bright fringe in the medium lies where the fifth dark fringe lies in air. The refractive index of the medium is nearly:
1. Option A: $1.78$
2. Option B: $1.25$
3. Option C: $1.59$
4. Option D: $1.69$
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Question 36 (NEET 2017, Q126)
Electric Charges and FieldsHard
Suppose the charge of a proton and an electron differ slightly. One of them is -e, the other is $(e + \Delta e)$ . If the net electrostatic force and gravitational force between two hydrogen atoms placed at a distance $d$ apart are zero, then the value of $\Delta e$ is of the order of: (Given: mass of hydrogen atom $m_h = 1.67 \times 10^{-27}\,\text{kg}$ )
1. Option A: $10^{-47}\,\text{C}$
2. Option B: $10^{-20}\,\text{C}$
3. Option C: $10^{-23}\,\text{C}$
4. Option D: $10^{-37}\,\text{C}$
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Correct answer: (D) $10^{-37}\,\text{C}$
Explanation
For equilibrium: $F_e = F_g$ $\frac{1}{4\pi\varepsilon_0}\frac{(\Delta e)^2}{d^2} = \frac{Gm_H^2}{d^2}$ $9 \times 10^9 (\Delta e)^2 = 6.67 \times 10^{-11}(1.67 \times 10^{-27})^2$ Solving: $\Delta e \approx 10^{-37}\,\text{C}$
Question 37 (NEET 2017, Q127)
Thermal Properties of MatterMedium
Two rods $A$ and $B$ of different materials are welded together as shown in the figure. Their thermal conductivities are $K_1$ and $K_2$ . The thermal conductivity of the composite rod will be:
1. Option A: $2(K_1+K_2)$
2. Option B: $\dfrac{K_1+K_2}{2}$
3. Option C: $\dfrac{3(K_1+K_2)}{2}$
4. Option D: $K_1+K_2$
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Correct answer: (B) $\dfrac{K_1+K_2}{2}$
Explanation
The rods are connected in parallel for heat flow. Total heat current: $H = \frac{K_1A(T_1-T_2)}{d} + \frac{K_2A(T_1-T_2)}{d}$ If equivalent conductivity is $K_{eq} $for total area$ 2A $:$ $H = \frac{K_{eq}(2A)(T_1-T_2)}{d}$ $Comparing:$ $K_{eq} = \frac{K_1+K_2}{2}$ $
Question 38 (NEET 2017, Q128)
Dual Nature of Radiation and MatterMedium
The photoelectric threshold wavelength of silver is $3250 \times 10^{-10}\,\text{m}$ . The velocity of the electron ejected from a silver surface by ultraviolet light of wavelength $2536 \times 10^{-10}\,\text{m}$ is: (Given: $h = 4.14 \times 10^{-15}\,\text{eV s}$ and $c = 3 \times 10^8\,\text{m/s}$ )
1. Option A: ≈ 0.3 × 10⁶ ms⁻¹
2. Option B: ≈ 6 × 10⁵ ms⁻¹
3. Option C: ≈ 0.6 × 10⁶ ms⁻¹
4. Option D: ≈ 61 × 10³ ms⁻¹
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Question 39 (NEET 2017, Q129)
WavesMedium
Two cars moving in opposite directions approach each other with speeds of $22\,\text{m/s}$ and $16.5\,\text{m/s}$ respectively. The driver of the first car blows a horn having frequency $400\,\text{Hz}$ . The frequency heard by the driver of the second car is: (Velocity of sound $= 340\,\text{m/s}$ )
1. Option A: $448\,\text{Hz}$
2. Option B: $350\,\text{Hz}$
3. Option C: $361\,\text{Hz}$
4. Option D: $411\,\text{Hz}$
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Correct answer: (A) $448\,\text{Hz}$
Explanation
Using Doppler effect: $f' = f\left(\frac{v+v_o}{v-v_s}\right)$ $f' = 400\left(\frac{340+16.5}{340-22}\right)$ $f' \approx 448\,\text{Hz}$
Question 40 (NEET 2017, Q130)
Work, Energy and PowerMedium
Consider a drop of rain water having mass $1\,\text{g}$ falling from a height of $1\,\text{km}$ . It hits the ground with a speed of $50\,\text{m/s}$ . Take $g$ constant with a value $10\,\text{m/s}^2$ . The work done by (i) gravitational force and (ii) resistive force of air is:
1. Option A: (i) $10\,\text{J}$ (ii) $-8.75\,\text{J}$
2. Option B: (i) $-10\,\text{J}$ (ii) $-8.25\,\text{J}$
3. Option C: (i) $1.25\,\text{J}$ (ii) $-8.25\,\text{J}$
4. Option D: (i) $100\,\text{J}$ (ii) $8.75\,\text{J}$
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Correct answer: (A) (i) $10\,\text{J}$ (ii) $-8.75\,\text{J}$
Explanation
Mass: $m = 1\,\text{g} = 10^{-3}\,\text{kg}$ Height: $h = 1000\,\text{m}$ Work done by gravity: $W_g = mgh$ $W_g = 10^{-3} \times 10 \times 1000 = 10\,\text{J}$ Final kinetic energy: $K_f = \frac{1}{2}mv^2$ $K_f = \frac{1}{2}(10^{-3})(50)^2 = 1.25\,\text{J}$ Using work-energy theorem: $W_g + W_{air} = K_f$ $10 + W_{air} = 1.25$ $W_{air} = -8.75\,\text{J}$
Question 41 (NEET 2017, Q131)
Electromagnetic WavesMedium
A spherical black body with a radius of $12\,\text{cm}$ radiates $450\,\text{W}$ power at $500\,\text{K}$ . If the radius were halved and the temperature doubled, the power radiated in watt would be:
1. Option A: $1800$
2. Option B: $225$
3. Option C: $450$
4. Option D: $1000$
The answer and explanation for this question are in NEET MIND Premium.
Question 42 (NEET 2017, Q132)
Electrostatic Potential and CapacitanceMedium
The diagrams below show regions of equipotentials. A positive charge is moved from $A$ to $B$ in each diagram. Identify the correct statement regarding the work required.
1. Option A: Maximum work is required to move $q$ in figure (b)
2. Option B: Maximum work is required to move $q$ in figure (c)
3. Option C: In all the four cases the work done is the same
4. Option D: Minimum work is required to move $q$ in figure (a)
The answer and explanation for this question are in NEET MIND Premium.
Question 43 (NEET 2017, Q133)
System of Particles and Rotational MotionMedium
Which of the following statements are correct? (a) Centre of mass of a body always coincides with the centre of gravity of the body. (b) Centre of mass of a body is the point at which the total gravitational torque on the body is zero. (c) A couple on a body produces both translational and rotational motion in a body. (d) Mechanical advantage greater than one means that small effort can be used to lift a large load.
1. Option A: (c) and (d)
2. Option B: (b) and (d)
3. Option C: (a) and (b)
4. Option D: (b) and (c)
The answer and explanation for this question are in NEET MIND Premium.
Question 44 (NEET 2017, Q134)
GravitationHard
If $\theta_1$ and $\theta_2$ are the apparent angles of dip observed in two vertical planes at right angles to each other, then the true angle of dip $\theta$ is given by:
1. Option A: $\tan^2\theta = \tan^2\theta_1 - \tan^2\theta_2$
2. Option B: $\cot^2\theta = \cot^2\theta_1 + \cot^2\theta_2$
3. Option C: $\tan^2\theta = \tan^2\theta_1 + \tan^2\theta_2$
4. Option D: $\cot^2\theta = \cot^2\theta_1 - \cot^2\theta_2$
The answer and explanation for this question are in NEET MIND Premium.
Question 45 (NEET 2017, Q135)
NucleiHard
Radioactive material $A$ has decay constant $8\lambda$ and material $B$ has decay constant $\lambda$ . Initially they have the same number of nuclei. After what time will the ratio of number of nuclei of material $B$ to that of material $A$ be $\dfrac{1}{e}$ ?
1. Option A: $\dfrac{1}{9\lambda}$
2. Option B: $\dfrac{1}{\lambda}$
3. Option C: $\dfrac{1}{7\lambda}$
4. Option D: $\dfrac{1}{8\lambda}$
Show answer & explanationHide answer & explanation
Correct answer: (C) $\dfrac{1}{7\lambda}$
Explanation
Radioactive decay law: $N = N_0e^{-\lambda t}$ For materials $A $and$ B $:$ $N_A = N_0e^{-8\lambda t}$ $N_B = N_0e^{-\lambda t}$ $Given:$ $\frac{N_B}{N_A} = \frac{1}{e}$ $e^{7\lambda t} = e^{-1}$ $Taking logarithm:$ $7\lambda t = 1$ $t = \frac{1}{7\lambda}$ $

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