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Grade 12 Physics national exam, 2011 E.C. (2019 G.C.)

43 questions · 120 minutes. The first 5 answers are shown with explanations; sit the whole paper timed in the app to get your score and the textbook page behind every question.

1. 1.Which part of a scientific report discusses the accuracy of measurements taken?
   • A. Aim
   • B. Theory
   • C. Methods
   • D. Results
   Answer: D. The key idea is that the results section presents the measurements collected in an experiment. This section lets the reader examine the measurements and judge their accuracy, so D is correct. A states the purpose; B gives the scientific ideas; C explains how the experiment was done. Textbook: Grade 11, unit 6 · section 6.4.
2. 2.Two forces exerted on a block as shown in the figure below. What is the horizontal component of the net force? [Figure: A rectangular block is shown. From its top-left corner, a force vector of magnitude 50 N is directed upward and to the left, making an angle of 53° with the horizontal line extending to the left. From its top-right corner, a force vector of magnitude 20 N is directed upward and to the right, making an angle of 37° with the horizontal line extending to the right.]
   • A. 70 N, East
   • B. 30 N, West
   • C. 14 N, West
   • D. 28 N, West
   Answer: C. The key idea is to add the horizontal parts of the forces, taking their directions into account. The leftward part is $50(0.6)=30\,\mathrm{N}$ and the rightward part is $20(0.8)=16\,\mathrm{N}$, so the net is $30-16=14\,\mathrm{N}$ West. A is wrong because it adds the full force sizes and ignores their directions. B is wrong because it subtracts the full force sizes instead of their horizontal parts. D is wrong because the horizontal parts give $14\,\mathrm{N}$, not $28\,\mathrm{N}$. Textbook: Grade 11, unit 2 · section 2.3.
3. 3.What is the magnitude of the resultant velocity for a bird flying first at a speed of 10 m/s North East and then flying to South at a speed of 8 m/s?
   • A. 7,13 m/s
   • B. 16.6 m/s
   • C. 12.8 m/s
   • D. 7.07 m/s
   Answer: A. Resolving the velocities into components, we have v_1 = (10*cos(45°), 10*sin(45°)) = (7.07, 7.07) m/s and v_2 = (0, -8) m/s. The resultant velocity is v = (7.07, -0.93) m/s, which has a magnitude of sqrt(7.07^2 + (-0.93)^2) ≈ 7.13 m/s. = C X A B θ =900 θ A B Textbook: Grade 11, unit 2 · section 2.3.
4. 4.Let and , where is the smaller angle between and when they are drawn with their tails at the same point. Which of the following is NOT true? . = A B 0 . = A C 0
   • D. / / = C / // / sin θ A B − = C X B A
   Answer: A. The key idea is that the dot product depends on the cosine of the angle, while the cross product is perpendicular to both vectors. Since $\vec{C}=\vec{A}\times\vec{B}$, $\vec{A}\cdot\vec{B}=|\vec{A}||\vec{B}|\cos\theta$, which is not zero because $\theta\ne90^\circ$; so A is not true. B is true because $\vec{A}$ is perpendicular to $\vec{C}$. C is true because $|\vec{C}|=|\vec{A}||\vec{B}|\sin\theta$. D is true because reversing the order of a cross product changes its sign: $\vec{B}\times\vec{A}=-\vec{C}$. Textbook: Grade 11, unit 2 · section 2.4.
5. 5.A driver of an automobile travelling at a constant speed of 20 m/s suddenly applies a brake and the automobile comes to rest in 2.0 seconds after skidding for a certain distance. What is the length of the skid distance?
   • A. 400 m
   • B. 10 m
   • C. 40 m
   • D. 20 m
   Answer: D. The key idea is that for constant acceleration, distance equals average speed times time. The average speed is $(20+0)/2=10\,\mathrm{m/s}$, so the skid distance is $(10\,\mathrm{m/s})(2.0\,\mathrm{s})=20\,\mathrm{m}$. A is wrong because $400\,\mathrm{m}$ is far greater than the distance travelled while braking. B is wrong because it is half the calculated distance. C is wrong because it is twice the calculated distance. Textbook: Grade 11, unit 3 · section 3.2.

1. 6.- From D(6,12), a straight line descends to point E(12,0) on the horizontal axis.]
   
   • A. Between C and D, the motion is with constant acceleration. 4m/s2
   • B. Between B and C, the acceleration is
   • C. Between D and E, the motion is with constant positive acceleration.
   • D. Total displacement is 84m.
   Answer: D. The total displacement is the area under the velocity-time graph, which consists of four sections: Area = 0.5*2*4 + 0.5* (4+12)*1 + 3*12 + 0.5*6*12 = 4 + 8 + 36 + 36 = 84 m. Textbook: Grade 11, unit 3 · section 3.3.
2. 7.An object of mass M is set in a vertical circular motion. The tension T from the rope keeps the object in a circular path with speed v. Where does the rope experience a maximum tension?
   • A. At the top of the circle
   • B. At the bottom of the circle 45∘
   • C. When the object is at half of the circle
   • D. When it is at to the vertical line
   Answer, explanation and textbook page: open in the app.
3. 8.A shell is fired from a gun, whose barrel is inclined at an angle to the horizontal. During the flight, the shell explodes in air into fragments. The center of mass of different fragments will follow
   • A. a horizontal straight line
   • B. a vertical straight line
   • C. a parabola
   • D. an unpredictable path
   Answer, explanation and textbook page: open in the app.
4. 9.A 5 kg mass pushed upward along an inclined plane of inclination with constant force F. If the acceleration 1.0 m/s2 of the block for this motion is and the plane is assumed to be friction less, what is the magnitude of the constant force F?
   • A. 5.0 N
   • B. 25.0 N
   • C. 20.0 N
   • D. 30.0 N
   Answer, explanation and textbook page: open in the app.
5. 10.A ball of mass M moves with speed V in the + x-direction. It explodes into two pieces that go off at angles and θ 1 θ 2 , as shown below. What are the magnitude of the momenta of the two pieces?. [Figure: A diagram shows a ball of mass M moving horizontally to the right along a straight line. At an explosion m 1 θ 1 m 2 θ point, the trajectory branches into two paths: one with mass labeled moving along an arrow directed upwards and to the right at an angle relative to the horizontal line, and another with mass labeled moving along an arrow directed downwards and to the right at an angle relative to the horizontal line.] 2 sin(θ +θ ) 1 2 MV cos θ 2 p = 2 sin(θ +θ ) 1 2 MV cos θ sin(θ +θ ) 1 2 MV sin θ sin(θ +θ ) 1 2 MV sin θ
   • A. , and
   • B. , and p = 1 1 p = 1 2 p = 2 1 cos(θ +θ ) 1 2 MV cos θ 2 p cos(θ +θ ) 1 2 MV cos θ 1 = 1 MV tan θ = 2 MV tan θ = 1 = 2
   • C. , and
   • D. , and p 2 p 1 p
   Answer, explanation and textbook page: open in the app.
6. 11.The rate of change of momentum of the raindrop can be given by u In this expression what does represent?
   • A. The velocity of the extra mass added to the raindrop
   • B. The velocity of the raindrop
   • C. The velocity of the loss in mass of raindrop
   • D. The rate of change of the velocity for combined system
   Answer, explanation and textbook page: open in the app.
7. 12.Which of the following is equal to the amount of work required to stop a moving object ?
   • A. the mass of the object times its acceleration
   • B. the kinetic energy of the object
   • C. the square of the velocity of the object
   • D. the mass of the object times its velocity
   Answer, explanation and textbook page: open in the app.
8. 14.In which of the following case is no work done by a dissipative force?
   • A. When a parachute jump from a plane
   • B. For a freely falling object
   • C. On a racing car that moves in a desert
   • D. When someone slides a box on a horizontal rough surface.
   Answer, explanation and textbook page: open in the app.
9. 15.Five beads of equal mass are fixed on a rigid light rod that is free to rotate about a frictionless vertical bearing. The arrangement is such that, four of them are placed at 0.25 m and the fifth one is at 0.5m from the axis of rotation. The rotational kinetic energy is 144J when the beads were rotating with angular speed of 48rad/s. What is the mass of each bead?
   • A. 0.25Kg
   • B. 0.5Kg
   • C. 0.75 Kg
   • D. 1Kg
   Answer, explanation and textbook page: open in the app.
10. 16.A thin circular ring of mass M and radius r and moment of inertia is rotating about its axis with a constant ω angular velocity . Two objects each of mass m, are attached gently to the opposite ends of a diameter of the ring. What would be the angular velocity of the wheel ? (M+2m) ω(M+2m) ωM
    • B. (M+m) M ω(M+2m)
    • D. ωM (M+2m)
    Answer, explanation and textbook page: open in the app.
11. 17.In a playing room a turn table of radius 2m has moment of inertia and is rotating about a frictionless vertical axel. When a boy of mass 50Kg stands near the rim, the system rotates with angular speed 3rad/s. The boy walks towards the center and stands at 1m from the axel. What is the final angular speed of the system?
    • A. 3rad/s
    • B. 2.5rad/s
    • C. 5.4rad/s
    • D. 4.5rad/s
    Answer, explanation and textbook page: open in the app.
12. 18.Two forces and are acting on a particle of mass m. What is the magnitude and direction of a force that balances the two? = Feq 1270 = Feq 1430
    • A. 7N at counterclockwise from
    • B. 5N at counterclockwise from F1 F2 = Feq 1270 = Feq 1430
    • C. 7N at counterclockwise from
    • D. 5N at counterclockwise from F2 F1
    Answer, explanation and textbook page: open in the app.
13. 20.Which of the following statement is correct about elastic behavior of materials?
    • A. For sufficiently small stress, stress is proportional to strain.
    • B. In tensile stress the force is parallel to the cross-sectional area, where as in shear stress, the force is perpendicular to the area.
    • C. All materials do not necessarily have elastic limit.
    • D. With plastic materials, the body goes to original dimensions after removal of the force that caused deformation.
    Answer, explanation and textbook page: open in the app.
14. 21.Water flows at a rate of 0.4 litter per second through garden hose of inside diameter 4.0 cm. The nozzle of the π = 3.14 hose is a circular opening of diameter 2.0 cm. What is the speed of the water when it emerges? ( )
    • A. 0.32 m/s
    • B. 1.27 m/s
    • C. 3.2 m/s
    • D. 12.7 m/s
    Answer, explanation and textbook page: open in the app.
15. 22.How much heat would be absorbed by 2g of ice at 0 c dropped into water at 0 c, to melt it totally to water at 0 c? (Latent heat of melting, L = 340,000J/Kg )
    • A. 680J
    • B. 840J
    • C. 340J
    • D. 420J
    Answer, explanation and textbook page: open in the app.
16. 23.The direction of heat flow is from:
    • A. high pressure to low pressure
    • B. high temperature to low temperature
    • C. high density to low density
    • D. a point of higher emissivity to lower one
    Answer, explanation and textbook page: open in the app.
17. 24.External force of 220N applied on a piston of a cylinder containing 1.25g of ammonia gas move 10cm as shown in the diagram below. Assuming adiabatic process, what is the rise in temperature of the gas? (Specific heat K ∘ capacity of ammonia, c = 2200J/Kg ) [Figure: A horizontal cylinder containing gas with a piston inside. An external force arrow labeled 'F = 220N' points to the left against the piston rod. A horizontal dimension below the piston indicates a displacement of '10cm' to the left between dashed reference lines.] K ∘ K ∘
    • A. 4
    • B. 8 K ∘ K ∘
    • C. 0.004
    • D. 0.008
    Answer, explanation and textbook page: open in the app.
18. 25.Which of the following statement is correct? (Here is the density of an ideal gas, is the mass of the gas and is speed of particles ) ρ⟨c ⟩ 2 1 2
    • A. P(pressure of an ideal gas ) =
    • B. For a mixture of two gases in equilibrium in a container, ⟩ 1 2 ⟨c ⟩ 2 2 ⟨c = ρ 1 ρ 2 ⟩ 1 2 ⟨c ⟩ 2 2
    • C. For a mixture of two gases in equilibrium in a container, = ρ 1 ρ 2 ⟨c
    • D. For a mixture of two different gases with equal partial pressure and equal number of molecules in a ⟨c ⟩ 2 2 ⟨c ⟩ 1 2 = m 1 m 2 container, .
    Answer, explanation and textbook page: open in the app.
19. 26.Which of the following statement is NOT correct?
    • A. No process is possible in which there is an overall decrease in the entropy of the universe.
    • B. The spontaneous transfer of energy from cooler body to a hotter body is not possible.
    • C. Spreading out of random kinetic energy through heating does not represent an overall increase in entropy.
    • D. The complete conversion of energy from a hot source into work is not possible.
    Answer, explanation and textbook page: open in the app.
20. 27.Which one of the following is not an example of simple harmonic motion?
    • A. A mass attached to a spring system oscillating in horizontal direction to the surface of the Earth
    • B. Oscillation of simple pendulum
    • C. Rotation of second pointer in hand watch
    • D. A mass attached to a spring system oscillating in vertical direction to the surface of the Earth
    Answer, explanation and textbook page: open in the app.
21. 28.Travelling wave is given by the equation , where is the wave number and is the angular frequency. What is the distance that the wave travels in the time ?
    • A. full wavelength
    • B. half the wavelength
    • C. a quarter of the wavelength
    • D. at the origin
    Answer, explanation and textbook page: open in the app.
22. 29.A 50 cm pipe is open at one end and closed at the other end. When air is blow at 150 Hz. What is the velocity of the sound along the pipe?
    • A. 150 m/s
    • B. 100 m/s
    • C. 330 m/s
    • D. 300 m/s
    Answer, explanation and textbook page: open in the app.
23. 30.In Young's double slit experiment, if the slit separation is 1.2mm and the average spacing of the bright fringes observed on a screen placed 4m away from the source is 2mm. What is the wavelength of the light source?
    • A. 550nm
    • B. 600nm
    • C. 630nm
    • D. 750nm
    Answer, explanation and textbook page: open in the app.
24. 31.The colors seen from soap bubbles and oil slicks are a manifestation of thin film interference. What is the cause of this interference?
    • A. Interference from refraction of light
    • B. Interference from reflection of light from the two surfaces of the film
    • C. Interference from diffraction of light
    • D. Interference from superposition of lights that are incident and reflected
    Answer, explanation and textbook page: open in the app.
25. 32.Two like charges of value q are fixed at x= a and x= -a as shown in the diagram below. q 0 If a test charge is released at y = b, which path will it follow? [Figure: A coordinate system with the horizontal x-axis and vertical y-axis. Two equal charges of value q are positioned on the x-axis at coordinates (-a, 0) and (a, 0). A test charge labeled q₀ is located on the y-axis at (0, b), with dashed lines connecting it to both charges at (-a, 0) and (a, 0).]
    • A. It stays at y = b
    • B. along a line y = − x + a b b y = x + a b b
    • C. along a line
    • D. along y- axis
    Answer, explanation and textbook page: open in the app.
26. 33.Two equal and opposite charges are located along x-axis at −2.0 cm and +2.0 cm as shown in the figure below. How much would be the electric potential at the origin? [Figure: A horizontal line showing two charges: a charge of $-4\,\mu\text{C}$ located at -2 cm to the left of the origin (labeled O), and a charge of $+4\,\mu\text{C}$ located at +2 cm to the right of the origin.]
    
    • A. Zero
    • B. 1.8 MV
    • C. 3.6 MV
    • D. 4.5 MV
    Answer, explanation and textbook page: open in the app.
27. 34.A sheet of polythene ($\varepsilon_r = 2.3$) and 0.25 mm thick is to be used in a capacitor by sandwiching it between two sheets of aluminum foil. What area must the sheets have if the capacitor is to have a capacitance of $0.5\,\mu\text{F}$?
    • A. 12 m$^2$
    • B. 6.14 m$^2$
    • C. 0.6 m$^2$
    • D. 0.12 m$^2$
    Answer, explanation and textbook page: open in the app.
28. 35.A metal rod is measured to have a resistance R. If the same metal rod is stretched to reduce its radius by half without affecting its density, what is its new resistance?
    • A. 2R
    • B. 4R
    • C. 8R
    • D. 16R
    Answer, explanation and textbook page: open in the app.
29. 36.The statement of Kirchoff's point rule follows from:
    • A. conservation of charge
    • B. conservation of energy
    • C. Ohm's law
    • D. dependence of resistance on temperature
    Answer, explanation and textbook page: open in the app.

1. 37.Across the horizontal diagonal between the left and right junctions is a galvanometer labeled 'G' connected in series with a resistor labeled 'R4'.] = R 2 R 1 R 4 R 3
   
   • A. The bridge is balanced when = R 3 R R 1 R
   • B. The bridge balance condition is given by . x 2 3 R x 4 R 1
   • C. = R R = R 3 R x R 4 R 2
   Answer, explanation and textbook page: open in the app.
2. 38.What is the expression of the centripetal acceleration of a particle of charge $q$ and mass $m$ moving in a uniform magnetic field $\mathbf{B}$ on a circle of radius $r$ if $\mathbf{B}$ is perpendicular to the particle's direction of motion?
   • A. $\frac{qB}{m}$
   • B. $\frac{2qB}{mr}$
   • C. $\frac{q^2B^2}{m}r$
   • D. $\frac{q^2B^2}{m^2}r$
   Answer, explanation and textbook page: open in the app.
3. 39.Two long wires of $10\,\text{m}$ in length carries a current of $2.0\,\text{A}$ and $0.5\text{A}$ in the same direction. The wires are separated by $4.0\,\text{cm}$. What is the magnetic force that the wires exerted on each other?
   • A. $5\times10^{-5}\,\text{N}$
   • B. $5\times10^{-6}\,\text{N}$
   • C. $5\times10^{-7}\,\text{N}$
   • D. $4\times10^{-6}\,\text{N}$
   Answer, explanation and textbook page: open in the app.
4. 40.Lenz's law in electromagnetic induction follows from which law of conservation ?
   • A. charge
   • B. energy
   • C. momentum
   • D. mass
   Answer, explanation and textbook page: open in the app.
5. 41.A rectangular loop of area is placed in a magnetic field that is changing at a rate of 100T/s. If the normal 60∘ of the loop makes angle with the magnetic field, what is the magnitude of induced emf?
   • A. 80V
   • B. 40V
   • C. 20V
   • D. 34.64V
   Answer, explanation and textbook page: open in the app.

1. 42.Two sinusoidal waveforms are shown: a solid curve labeled 'Voltage' passing through the origin (0, 0) and 90∘ going positive, and a dashed curve labeled 'Current' which is shifted to the right by a quarter period ( phase lag behind the voltage wave), reaching its first positive peak a quarter cycle after the voltage waveform peaks.]
   • A. inductor
   • B. capacitor
   • C. resistor
   • D. diode
   Answer, explanation and textbook page: open in the app.
2. 43.A series circuit consisting of resistor and capacitor of capacitive reactance are connected to alternating source of voltage(rms) 100V. What is the average power output and power factor of the circuit?
   • A. 141.4W, 0.8
   • B. 200W, 0.8
   • C. 70.7W, 0.707
   • D. 100W, 0.707
   Answer, explanation and textbook page: open in the app.
3. 44.When ultraviolet light is shone on a clean metal surface the surface will emit electrons. What is the necessary precondition for electrons to be ejected from the metal surface is ?
   • A. The intensity of light must be high enough
   • B. The minimum energy required to release the electron is the same as the work function of the metal
   • C. The wave length of the light has to be greater than that of ultraviolet light.
   • D. The frequency of the metal has to be less than that of ultraviolet light.
   Answer, explanation and textbook page: open in the app.
4. 45.Complete the following equation which represents a nuclear fission reaction. What is the particle represented by 0 1 n → Rb + 95 139 Cs + 2X + energy 235 U + X? ?
   • A. electron
   • B. proton
   • C. neutron
   • D. alpha particle
   Answer, explanation and textbook page: open in the app.