Gobezoch › Past exams › Physics
Grade 12 Physics national exam, 2009 E.C. (2017 G.C.)
26 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.The range of cannon-ball fired horizontally from a laboratory table is equal to 8/3 times the height of the table. What is the direction of velocity vector of the projectile as it strikes the ground?
- A. 45° from the horizontal
- B. 53° from the horizontal
- C. 60° from the horizontal
- D. 37° from the horizontal
Answer: D. The impact direction depends on the horizontal and vertical speeds at the ground. Since $R=8h/3$, the angle below the horizontal has $\tan\theta=v_y/v_x=2h/R=3/4$, giving $\theta\approx37^\circ$. A, $45^\circ$, is too large; B, $53^\circ$, is too large; C, $60^\circ$, is too large. Textbook: Grade 12, unit 2 · section 2.1.
Galileo carried out a ᓼthoughtᓼ experiment on motion. The line between A and B represents a surface and the center of the ball is placed at A. what would happen in each of the three situations shown in the figure below, without friction when the ball is released? [Figure: Three hand-drawn panels labelled a, b and c. In each, a small shaded ball sits at a point labelled A on the left, and a horizontal dashed line runs from A rightwards to a point labelled B. Panel (a): from the ball a solid curve dips below the dashed line as a symmetric U-shaped valley and rises back up to meet the dashed line exactly at B on the right. Panel (b): the solid curve dips below the dashed line in a shallower valley, crosses the dashed line at B and continues rising steeply upward past B (the far side of the valley is much less steep, so the rising track carries on above and beyond B).
- 2.Panel (c): the solid curve drops from the ball and then runs flat and horizontal to the right indefinitely, with a straight arrow above it pointing right; the label at the right reads "B at ∞" (B at infinity).]
- A. The ball would never reach point B in all instances.
- B. The ball would reach B in all instances even if point B keeps on receding to infinity in (c).
- C. The ball would reach point B in (a) and (b) and not in (c).
- D. The ball would reach point B only in (a).
Answer: B. Textbook: Grade 11, unit 3 · section 3.3.
A uranium atom initially at rest has a mass of 2 units and spontaneously disintegrated into two fragments. One of the fragments has a mass of 0.8 units and moves at a speed of 24m/s as shown in figure below. What is the speed of the second fragments? [Figure: A photographed hand-drawn sketch. On the left a shaded oval (the parent nucleus) sits on a long M = 2 u = 0 horizontal reference line, labelled above as units, . The horizontal line runs to the right. At a point 30∘ on that line the two fragment tracks cross it. One arrow goes up and to the right, making an angle of above m , v 2 2 53∘ the horizontal line, ending in a shaded oval labelled .
- 3.The other arrow goes down and to the left-of- vertical, making an angle of below the horizontal line on the left side, passing through a shaded oval m = 1 0.8 v = 1 24 labelled units, m/s and continuing to an arrowhead at the lower left.]
- A. 25.6m/s
- B. 21.3m/s
- C. 16m/s
- D. 14.8m/s
Answer: C. Textbook: Grade 11, unit 3 · section 3.5. - 4.A 1kg object explodes and breaks up into three pieces. One piece has a mass of 400g and has a velocity of (15i + 10j)m/s. a second piece has a mass of 250g and has a velocity of (25i ᓼ 10j)m/s. What is the velocity of the third piece?
- A. (-4.3i + 35j)m/s
- B. (-35i ᓸ 4.3j)m/s
- C. (35i ᓼ 4.3j)m/s
- D. (-35i ᓼ 4.3j)m/s
Answer: B. During an explosion, total momentum is conserved; if the object starts at rest, the three momenta add to zero. The third piece has mass $1-0.400-0.250=0.350\,\mathrm{kg}$; using the given velocities, its components are $v_x=-(0.400\times15+0.250\times25)/0.350=-35\,\mathrm{m/s}$ and $v_y=-(0.400\times10-0.250\times10)/0.350=-4.3\,\mathrm{m/s}$, giving option B. A has the wrong components. C has the wrong horizontal direction. D has the wrong vertical direction. Textbook: Grade 11, unit 3 · section 3.3. - 5.Which of the following statements is not correct?
- A. Dynamic equilibrium is an equilibrium in which a body is moving at steady velocity without net force or torque acting on it.
- B. Static equilibrium is an equilibrium in which a body is at rest without net force or torque acting on it.
- C. Couples are set of forces with a resultant torque but no net force.
- D. The necessary and sufficient condition for equilibrium of a rigid body is to have the sum of all torques acting on it is zero.
Answer: D. A rigid body is in equilibrium only when both its net force and its net torque are zero. D is not correct because zero total torque alone is not sufficient; the net force must also be zero. A correctly describes dynamic equilibrium, and B correctly describes static equilibrium. C correctly describes a couple, which turns an object without a net force. Textbook: Grade 10, unit 3 · section 3.5.2. - 6.A spring with a spring constant of 300N/m is stretched 20cm in 2 seconds. What is the power applied to stretch the spring?
- A. 3W
- B. 6W
- C. 30KW
- D. 60KW
Answer, explanation and textbook page: open in the app. - 7.A 50KW machine is used to lift heavy objects to the top of a building under construction. If this machine is replace with a new machine of 100KW power, then which of the following statements is not true about the new machine?
- A. The new machine can raise objects with the same mass at twice the speed of the old machine.
- B. The new machine can raise objects with twice as much mass at the same speed as the old machine.
- C. The new machine takes twice as much time to do the same work as the old machine.
- D. The new machine can do twice as much work in the same time as the old machine.
Answer, explanation and textbook page: open in the app. - 8.Which of the following is correct about a work done for dissipative force?
- A. Path dependent
- B. The same as the loss in kinetic energy.
- C. The same as the gain in potential energy.
- D. The same as the potential energy stored in spring.
Answer, explanation and textbook page: open in the app. - 9.A disk of radius R with uniform distribution of mass M rotates about an axis perpendicular to its plane at the rim ω 2 with angular speed the moment of inertia of the disc about the axis through the center is1/2MR . What is the kinetic energy of the disk? 1/4MR ω 2 2 1/3MR ω 2 2
- B. 1/2MR ω 2 2 4/4MR ω 2 2
Answer, explanation and textbook page: open in the app. - 10.A pulley is rotating at a frequency of 20rev/min. a motor speeds up the wheel so that 30s later the frequency of the motion is 60rev/min. How far a point on the pool 0.30m from its center will has travelled during that period?
- A. 125.7m
- B. 0.13m
- C. 37.68m
- D. 4.2m
Answer, explanation and textbook page: open in the app. - 11.Which of the following statements is correct about the first condition of equilibrium?
- A. The net force on an object must be zero.
- B. The sum of all torques must be zero.
- C. Clockwise moments should balance counter clockwise moments.
- D. The torque produced by a force should be perpendicular to the force.
Answer, explanation and textbook page: open in the app. - 13.Which of the following refers to the definition of strain as a ratio?
- A. Extension to the original length.
- B. Force applied to area of the object normal to the force.
- C. Stress to Young modulus.
- D. Tensile to applied force.
Answer, explanation and textbook page: open in the app. - 14.Which of the following is the application of Pascalᓼs law?
- A. Hydraulic brake in vehicles.
- B. Siphon to remove fluids.
- C. Working of submarines.
- D. Sucking of liquid into a syringe.
Answer, explanation and textbook page: open in the app. - 15.If a precision of surveyor measured a distance of 500 meters /between two points in a village/ using a meter that has centimetre division on it, then what is the measurement result?
- A. 500m
- B. 500.0m
- C. 500.00m
- D. 500.000m
Answer, explanation and textbook page: open in the app.
From the figures given below, which one of them shows precise but not accurate measurements? T represents the true value. [Figure: Four photographed hand-drawn distribution graphs, one per option. Every graph has the same axes: the vertical axis is labelled "Number of readings" and the horizontal axis is labelled "Reading", with a single letter T marked as a tick position on the horizontal axis. Graph A: T is marked near the left of the axis; a tall, narrow, sharply peaked curve rises well to the right of T, clearly separated from it (narrow spread, displaced from the true value). Graph B: T is marked on the axis and the tall, narrow, sharply peaked curve sits directly over T (narrow spread, centred on the true value). Graph C: a broad, low, wide hump whose maximum lies a little to the left of T, its tail spreading past T to the right (wide spread, roughly straddling the true value).
- 16.Graph D: a broad, low, wide hump whose maximum lies well to the left of T, dying away just before T (wide spread, displaced from the true value).]
- A. Graph A: a tall narrow peak located well to the right of T.
- B. Graph B: a tall narrow peak centred on T.
- C. Graph C: a broad low hump whose maximum lies just to the left of T.
- D. Graph D: a broad low hump whose maximum lies well to the left of T.
Answer, explanation and textbook page: open in the app. - 17.If vector is 6m in the x-direction and vector is 8m in the y-direction. Then what is the value of the vector P q + p q ? m 136 450
- A. 10m at 53° from x-direction.
- B. at from x-direction. m 136 300
- C. 10m at 37° from x-direction.
- D. at from x-direction.
Answer, explanation and textbook page: open in the app. - 18.Given vectors and . What is the smaller angle between the vectors?
- A. 60°
- B. 53°
- C. 45°
- D. 30°
Answer, explanation and textbook page: open in the app. - 19.If $\vec{A}=\vec{x}\,\frac{\text{m}}{\text{s}}+3\,\frac{\text{m}}{\text{s}}\,\vec{z}$ and $\vec{B}=2\,\frac{\text{m}}{\text{s}}\,\vec{y}+3\,\frac{\text{m}}{\text{s}}\,\vec{z}$, then what is the value of $|\vec{A}\times\vec{B}|$?
- A. $\sqrt{10}\,\frac{\text{m}}{\text{s}}$
- B. $\sqrt{13}\,\frac{\text{m}}{\text{s}}$
- C. $7\,\frac{\text{m}}{\text{s}}$
- D. $\sqrt{130}\,\frac{\text{m}}{\text{s}}$
Answer, explanation and textbook page: open in the app. - 20.A cricketer throws a ball vertically upwards with initial speed of 20m/s. How long is it in the air before it returns to the cricketerᓼs hands?
- A. 2s
- B. 10s
- C. 1.5s
- D. 4s
Answer, explanation and textbook page: open in the app. - 22.The activity of radioactive substance reduces from $2000\mathrm{Bq}$ to $1000\mathrm{Bq}$ in $10^6$ seconds. What is the decay constant?
- A. $6.93\times10^5$, decay/s
- B. $6.93\times10^{-7}$, decay/s
- C. $2.00\times10^6$, decay/s
- D. $5.00\times10^{-7}$, decay/s
Answer, explanation and textbook page: open in the app. - 23.Which of the following phenomena clearly demonstrates the particle nature of light?
- A. Refraction of light by prism.
- B. The photoelectric effect.
- C. Diffraction of light by double slit.
- D. Dispersion of white light.
Answer, explanation and textbook page: open in the app. - 24.Which of the following statements is correct?
- A. Irreversible process is a process that can be reversed through finite change in the system.
- B. Complete conversion of energy from a hot source into work is possible.
- C. There are processes in which there is an overall decrease in entropy.
- D. Entropy is a measure of the amount of disorder.
Answer, explanation and textbook page: open in the app. - 25.A certain heat engine draws 500cal/s from a water bath at 27°C and rejects 400 calories to a reservoir at a lower temperature. What is the efficiency of this engine?
- A. 80%
- B. 75%
- C. 25%
- D. 20%
Answer, explanation and textbook page: open in the app. - 26.Three metals are in contact and in thermal equilibrium. The metals have different specific heat capacity. What can be concluded about the temperature of the metals?
- A. Since they have different specific heat capacity, they must have different temperature at thermal equilibrium.
- B. They must have the same temperature at thermal equilibrium.
- C. They must have different internal energy.
- D. They must have different kinetic energy.
Answer, explanation and textbook page: open in the app. - 27.Metal A has a coefficient of linear expansion that is three times the coefficient of linear expansion of metal B. How does their coefficient of areal expansion, Y, compare?
- B. Y = A 2Y B Y = A 3Y B Y = A 4Y B Y = A 6Y B
Answer, explanation and textbook page: open in the app. - 28.On an unknown scale x, the ice point temperature is 50°x and the steam-point temperature is 200°x. If the temperature is 60°C, then what is the reading in °x?
- A. 90°x
- B. 140°x
- C. 15°x
- D. 333°x
Answer, explanation and textbook page: open in the app.