49 questions. Try each one, then open the answer to check yourself and read the explanation.
If the total force acting on a particle is zero, the linear momentum will
Answer: B (be constant)
Zero resultant force means no change in momentum (Newton's second law), so the momentum stays constant.
The effect of a particle in a fluid attaining its terminal velocity is that the
Answer: A (weight is equal to the retarding force)
At terminal velocity the forces balance: the weight equals the total upward (retarding) force, so the acceleration is zero.
If the distance between two suspended masses 10kg each is tripled, the gravitational force of attraction between them is reduced by
Answer: B (one ninth)
F ∝ 1/d2, so tripling d makes the force (1/3)2 = 1/9 of its old value.
The diagram above shows the force-extension curve of a piece of wire. The energy stored when the wire is stretched from E to F is
Answer: C (7.5 × 10−3 J)
Energy = area under the graph from E (0.05 m, 0.1 N) to F (0.10 m, 0.2 N) = ½(0.1 + 0.2) × 0.05 = 7.5 × 10−3 J.
The diagram above shows the force (F) acting on an object through a distance (x). The work done on this object is expressed as
Answer: D (Fx/2 J)
Work done is the area under the force–distance graph, a triangle of base x and height F, so W = ½Fx = Fx/2.
A wheel and axle is used to raise a load of 500 N by the application of an effort of 250N. If the radii of the wheel and the axle are 0.4cm and 0.1 cm respectively, the efficiency of the machine is
Answer: B (50%)
VR = 0.4/0.1 = 4 and MA = 500/250 = 2, so efficiency = 2/4 × 100% = 50%.
Two forces each of 10N act on a body, one towards the north and the other towards the east. The magnitude and the direction of the resultant force are
Answer: A (10√2 N, 45°E)
R = √(102 + 102) = 10√2 N, and tan θ = 10/10 gives 45° between north and east (N45°E).
The hydrostatic blood pressure difference between the head and feet of a boy standing straight is 1.65 × 104 Nm−2. Find the height of the boy. [Density of blood = 1.1 × 103 kgm−3, g = 10ms−2]
Answer: D (1.5m)
h = P/(ρg) = 1.65 × 104 ÷ (1.1 × 103 × 10) = 1.5 m.
A body weighing 80N stands in an elevator that is about to move. The force exerted by the floor on the body as the elevator moves upwards with an acceleration of 5ms−2 is [g = 10ms−2]
Answer: B (120N)
Mass = 80/10 = 8 kg. R = m(g + a) = 8 × (10 + 5) = 120 N.
A copper cube weighs 0.25N in air, 0.17N when completely immersed in paraffin oil and 0.15N when completely immersed in water. The ratio of upthrust in oil to upthrust in water is
Answer: A (4:5)
Upthrust in oil = 0.25 − 0.17 = 0.08 N; in water = 0.25 − 0.15 = 0.10 N; ratio 0.08 : 0.10 = 4 : 5.
Which of the following is the correct shape of the velocity-time graph of a spherical steel ball dropped into a viscous fluid in a tall cylinder?
Answer: D (Graph D)
The ball speeds up quickly at first, then the viscous drag grows until it reaches a steady terminal velocity, so the curve rises and levels off (graph D).
A particle in circular motion performs 30 oscillations in 6 seconds. Its angular velocity is
Answer: A (10π rad s−1)
f = 30/6 = 5 Hz, so ω = 2πf = 10π rad s−1.
I. Temperature. II. Density of air molecules. III. Pressure. IV. Pitch.
Which of the above will affect the velocity of sound in air?
Answer: D (I and II only.)
The speed of sound in air depends on temperature and on the density of the air; pressure alone (at fixed temperature) and pitch do not change it.
A coin placed below a rectangular glass block of thickness 9 cm and refractive index 1.5 is viewed vertically above the block. The apparent displacement of the coin is
Answer: D (3cm)
Apparent depth = 9/1.5 = 6 cm, so the coin appears raised by 9 − 6 = 3 cm.
The phenomenon that makes sound persist when its source has been removed is known as
Answer: C (reverberation)
Reverberation is the persistence of sound in a room after the source stops, caused by many overlapping reflections.
A ray of light which strikes a glass slab from air at normal incidence passes through the slab
Answer: C (undeviated and undisplaced at a lower speed)
At normal incidence the ray does not bend, so it goes straight through without deviation or sideways displacement; it travels more slowly in glass.
The colours seen in soap bubbles are due to
Answer: A (interference)
Light reflected from the front and back surfaces of the thin soap film interferes; different thicknesses reinforce different colours.
The pressure of 3 moles of an ideal gas at a temperature of 27°C having a volume of 10−3m3 is [R = 8.3 J mol−1 K−1]
Answer: B (7.47 × 106 Nm−2)
P = nRT/V = 3 × 8.3 × 300 ÷ 10−3 = 7.47 × 106 N m−2.
To produce an enlarged and erect image with a concave mirror, the object must be positioned
Answer: C (between the principal focus and the pole)
Only an object inside the focal length of a concave mirror gives a virtual, erect, magnified image.
Blowing air over a liquid aids evaporation by
Answer: D (decreasing its vapour pressure.)
Moving air carries away the vapour above the liquid, lowering the vapour pressure there so more molecules can escape.
Which of the following eye defects can be corrected using a cylindrical lens?
Answer: A (Astigmatism)
Astigmatism comes from unequal curvature of the cornea in different directions; a cylindrical lens corrects curvature in one direction only.
The radiator of a motor car is cooled by
Answer: B (convection)
Air flowing through the radiator carries the heat away, which is cooling by (forced) convection.
Vibrations in a stretched spring cannot be polarized because they are
Answer: D (longitudinal waves.)
Only transverse waves can be polarized; vibrations along a stretched spring are longitudinal.
The time rate of loss of heat by a body is proportional to the
Answer: C (difference in temperature between the body and its surroundings)
Newton's law of cooling: the rate of heat loss is proportional to the excess temperature of the body over its surroundings.
The property that is propagated in a travelling wave is
Answer: B (energy)
A travelling wave carries energy from one place to another without carrying the medium along.
Which of the following is a characteristic of stationary waves?
Answer: C (They are formed by two identical waves travelling in opposite directions.)
A stationary wave forms when two identical waves travel in opposite directions and superpose. Antinodes have maximum displacement and nodes are half a wavelength apart.
A concave mirror of radius of curvature 40cm forms a real image twice as large as the object. The object distance is
Answer: A (30cm)
f = 20 cm and v = 2u. 1/u + 1/(2u) = 1/20 gives 3/(2u) = 1/20, so u = 30 cm.
If tension is maintained on a stretched string of length 0.6m, such that its fundamental frequency of 220Hz is excited, determine the velocity of the transverse wave in the string.
Answer: C (264ms−1)
For the fundamental, λ = 2L = 1.2 m, so v = fλ = 220 × 1.2 = 264 m s−1.
The energy stored in a capacitor of capacitance 10μF carrying a charge of 100μC is
Answer: B (5 × 10−4J)
E = Q2/(2C) = (100 × 10−6)2 ÷ (2 × 10 × 10−6) = 5 × 10−4 J.
An electric iron is rated 1000W, 230V. What is the resistance of its element?
Answer: C (52.9Ω)
R = V2/P = 2302/1000 = 52.9 Ω.
An electric cell with nominal voltage E has a resistance of 3Ω connected across it. If the voltage falls to 0.6E, the internal resistance of the cell is
Answer: C (2Ω)
The 3 Ω resistor gets 0.6E and the internal resistance the remaining 0.4E. With the same current, r = 3 × 0.4/0.6 = 2 Ω.
The electromagnetic wave that can produce a heating effect on the environment is
Answer: B (infrared rays)
Infrared radiation is the part of the spectrum we feel as heat; it warms whatever absorbs it.
From the diagram above, determine the value of the resistance X.
Answer: C (15Ω)
Total resistance = 12 V ÷ 2 A = 6 Ω, so the parallel pair is 6 − 2 − 1.5 = 2.5 Ω. 3X/(3 + X) = 2.5 gives X = 15 Ω.
Calculate the refractive index of the material for the glass prism in the diagram above.
Answer: A (√2)
The ray passes through symmetrically (minimum deviation) with A = 60° and D = 30°: n = sin((60 + 30)/2) ÷ sin(60/2) = sin 45° ÷ sin 30° = √2.
When connected to a mains of 250V, the fuse rating in the plug of an electric device of 1kW is
Answer: A (4A)
I = P/V = 1000 ÷ 250 = 4 A.
The eye controls the amount of light reaching the retina by adjusting the
Answer: D (iris.)
The iris changes the size of the pupil, letting in more or less light.
The electric field between two-point charges is shown in the diagram above. What types of charges are at X and Y?
Answer: C (Both X and Y are positive.)
Field lines point away from positive charges; here the lines leave both X and Y and bend away from each other, so both are positive.
A transistor is used in the amplification of signals because it
Answer: D (controls the flow of current.)
A transistor amplifies because a small current at the base controls a much larger current through the collector and emitter, so a weak signal is reproduced as a strong one.
A current of 0.5 A flowing for 3 h deposits 2g of a metal during electrolysis. The quantity of the same metal that would be deposited by a current of 1.5 A flowing in 1h is
Answer: C (2g)
Mass deposited ∝ It. 0.5 × 3 = 1.5 × 1, so the same charge passes and the same 2 g is deposited.
The particle that is responsible for nuclear fission in a nuclear reactor is
Answer: C (neutron)
Slow neutrons are absorbed by uranium-235 nuclei and make them split, releasing more neutrons that keep the chain reaction going.
The carbon-granule microphone works on the principle of change in
Answer: C (resistance)
Sound pressure squeezes the carbon granules, changing their resistance and so the current in the circuit.
The energy associated with the photon of a radio transmission at 3 × 105Hz is [h = 6.63 × 10−34 Js]
Answer: D (2.00 × 10−28 J)
E = hf = 6.63 × 10−34 × 3 × 105 ≈ 2.0 × 10−28 J.
From the generating station to each substation, power is transmitted at a very high voltage so as to reduce
Answer: C (heating in the coils)
At high voltage the current is small, so the I2R heating loss in the conductors is small.
The percentage of the original nuclei of a sample of a radioactive substance left after 5 half-lives is
Answer: D (3%)
After 5 half-lives the fraction left is (½)5 = 1/32 ≈ 3.1%, which is about 3%.
Which of the following graphs shows the correct vector diagram for the circuit above?
Answer: D (Diagram D)
In an inductor–resistor circuit VR is in phase with the current I, and VL leads I by 90°. Diagram D shows VR along I and VL at right angles, ahead of it.
Which of the following statements is true of the properties of a moving coil galvanometer?
Answer: D (There is a strong permanent magnet to give high magnetic flux.)
A sensitive galvanometer needs a strong magnet, many turns, a large coil area and weak hair springs; only D is true.
Pure silicon can be converted to a p-type material by adding a controlled amount of
Answer: D (trivalent atoms)
Trivalent atoms (e.g. boron) have one electron too few for the bonds, which creates holes: p-type.
2311Na + X → 209F + 42He
What particle is X in the reaction above?
Answer: D (Neutron)
Mass numbers: 23 + A = 20 + 4 gives A = 1. Atomic numbers: 11 + Z = 9 + 2 gives Z = 0. A particle with mass 1 and charge 0 is a neutron.
At what frequency would a capacitor of 2.5μF used in a radio circuit have a reactance of 250Ω?
Answer: A (800/π Hz)
XC = 1/(2πfC), so f = 1 ÷ (2π × 250 × 2.5 × 10−6) = 800/π Hz.