S3 Physics Practice Paper (Set 2): Pressure And Buoyancy, Density And Floating, Reflection And Refraction, Series And Parallel Circuits With Ohm Law, Work And Power, Heat Transfer And Specific Heat Capacity (with Answers)

S3 Physics Practice Paper (Set 2): Pressure and Buoyancy, Density and Floating, Reflection and Refraction, Series and Parallel Circuits with Ohm Law, Work and Power, Heat Transfer and Specific Heat Capacity (with answers)

2026-11-15

Junior Secondary Physics

S3 Physics paper Set 2 with full answers: pressure, buoyancy, density, optics, circuits, energy, heat; 24 parts, 100 marks, 60 minutes, for school exams and DSE basics.

Paper details　S3 Physics practice paper Set 2 with full answers: 100 marks, 60 minutes.

Pressure and Buoyancy

These questions cover pressure on solids, density, buoyancy and pressure in liquids. Take g = 10 N/kg.

#	Question	Answer and marking notes
1	A brick exerts a force of 240 N on the ground over a contact area of 0.04 square metres. Find the pressure on the ground in pascals and in kilopascals.	Answer: pressure = force divided by area = 240 divided by 0.04 = 6000 Pa, that is 6 kPa. For a fixed force, pressure is inversely proportional to area, so a smaller area gives a larger pressure.
2	A metal block has a mass of 216 g and a volume of 80 cm3. Find its density and suggest which metal it is most likely to be (aluminium 2.7, iron 7.8, copper 8.9 g/cm3).	Answer: density = mass divided by volume = 216 divided by 80 = 2.7 g/cm3, which matches aluminium, so the block is most likely aluminium.
3	A wooden block of mass 0.5 kg floats on water. Find the upthrust on the block and explain why it has that value.	Answer: a floating body at rest has upthrust equal to its weight, so upthrust = m times g = 0.5 times 10 = 5 N. If upthrust exceeded the weight, the block would rise until it displaced less water.
4	A diver descends to a depth of 12 m. Given the density of water is 1000 kg/m3, find the pressure due to the water in Pa and kPa.	Answer: pressure = rho times g times h = 1000 times 10 times 12 = 120000 Pa = 120 kPa. Pressure in a liquid depends only on depth, density and g, not on the shape of the container.

Density and Floating

These questions cover comparing densities, the floating condition and hollow objects. Take the density of water as 1.0 g/cm3.

#	Question	Answer and marking notes
5	A plastic block has mass 600 g and volume 750 cm3. Find its density and state whether it floats or sinks in water.	Answer: density = 600 divided by 750 = 0.8 g/cm3, which is less than 1.0 g/cm3, so the block floats. A body floats when its density is less than the liquid density and sinks when it is greater.
6	For the same block, what percentage of its volume is submerged when it floats, and what percentage stays above the surface?	Answer: for a floating body the ratio of displaced volume to total volume equals the ratio of its density to the liquid density, 0.8 divided by 1.0 = 80 percent. So 80 percent is submerged and 20 percent is above the surface.
7	Ice has a density of 0.92 g/cm3. What percentage of a floating ice block is submerged, and how does this relate to the effect of melting ice shelves on sea level?	Answer: the submerged fraction is 0.92 divided by 1.0 = 92 percent. Ice already floating displaces its own melted weight, so melting it leaves sea level unchanged; ice flowing into the sea from land, however, raises sea level.
8	An iron ball has mass 780 g and outer volume 200 cm3; the density of iron is 7.8 g/cm3. Find the average density of the ball and the volume of its cavity.	Answer: average density = 780 divided by 200 = 3.9 g/cm3. The iron itself occupies 780 divided by 7.8 = 100 cm3, so the cavity is 200 minus 100 = 100 cm3. The cavity lowers the average density, which is why a hollow iron ball can float.

Reflection and Refraction

These questions cover reflection at a plane mirror, the law of refraction and a concave mirror. Take the refractive index of air as 1.0.

#	Question	Answer and marking notes
9	A ray strikes a plane mirror with an angle of incidence of 35 degrees. Find the angle of reflection and the angle between the incident and reflected rays.	Answer: by the law of reflection the angle of reflection equals the angle of incidence, 35 degrees. The angle between the two rays is 35 plus 35 = 70 degrees. Angles are always measured from the normal.
10	A person stands 1.6 m in front of a plane mirror. How far is his image from him, and what is the distance after he moves 0.5 m closer?	Answer: a plane mirror image lies as far behind the mirror as the object is in front, so the image is 1.6 times 2 = 3.2 m away. After moving 0.5 m closer he is 1.1 m from the mirror and the image is 1.1 times 2 = 2.2 m away, that is 1 m nearer.
11	A ray passes from air into glass of refractive index 1.5 at an angle of incidence of 30 degrees. Find the angle of refraction to one decimal place and state whether the ray bends towards or away from the normal.	Answer: n = sin i divided by sin r, so sin r = sin 30 degrees divided by 1.5 = 0.5 divided by 1.5 which is about 0.333, giving r of about 19.5 degrees. Going from a less dense to a denser medium the light slows down and bends towards the normal.
12	A concave mirror has a radius of curvature of 30 cm. Find its focal length, and for an object 30 cm in front of the mirror find the image distance, the magnification and the nature of the image.	Answer: focal length f = R divided by 2 = 30 divided by 2 = 15 cm. The object is at 2f, so the mirror formula gives an image distance of 30 cm with magnification 1: an inverted, same-size real image at 2f in front of the mirror.

Series and Parallel Circuits with Ohm Law

These questions cover series and parallel circuits, Ohm law, electrical power and energy.

#	Question	Answer and marking notes
13	Resistors of 6 ohm and 9 ohm are connected in series to a 4.5 V supply. Find the total resistance, the current and the voltage across each resistor.	Answer: total resistance = 6 plus 9 = 15 ohm; current I = V divided by R = 4.5 divided by 15 = 0.3 A; the voltages are 1.8 V and 2.7 V, which add up to 4.5 V.
14	The same supply now feeds resistors of 6 ohm and 3 ohm in parallel. Find the equivalent resistance and explain why it is smaller than either branch.	Answer: 1/R = 1/6 plus 1/3, so R = (6 times 3) divided by (6 plus 3) = 2 ohm. Adding a parallel branch adds another path for current, so the total current rises while the voltage stays the same, which makes the equivalent resistance smaller than the smallest branch.
15	For the series circuit in part 1, the current is 0.3 A. Find the total electrical power used by the circuit.	Answer: P = V times I = 4.5 times 0.3 = 1.35 W. Checking with P = I squared times R, 0.3 squared times 15 also gives about 1.35 W.
16	The circuit runs for 600 seconds. Find the electrical energy used in joules and explain why the wires warm up slightly.	Answer: E = P times t = 1.35 times 600 = 809 J. As current flows, the resistance of the metal wire converts some electrical energy into internal energy, so the wire warms up. This Joule heating is exactly what appliances such as electric kettles rely on.

Work and Power

These questions cover work, power, efficiency and mechanical energy. Take g = 10 N/kg.

#	Question	Answer and marking notes
17	A worker pushes a crate horizontally with a force of 250 N through a distance of 12 m. Find the work done.	Answer: W = F times s = 250 times 12 = 3000 J. Only the component of force along the displacement does work; a force perpendicular to the displacement, such as carrying a case horizontally, does no work.
18	In the previous part the worker takes 20 s. Find the power output.	Answer: P = W divided by t = 3000 divided by 20 = 150 W. Power measures how fast work is done rather than how much: the same work done in less time means greater power.
19	A crane takes in 500 J of electrical energy and does 400 J of useful work lifting a load. Find its efficiency.	Answer: efficiency = useful work divided by energy input times 100 percent = 400 divided by 500 times 100 percent = 80 percent. The remaining 100 J is mostly lost as internal energy through friction and sound.
20	A ball of mass 2 kg is raised 5 m. Find the gain in potential energy; if it then falls freely from rest, what are its kinetic energy and speed on landing (ignoring air resistance)?	Answer: potential energy = mgh = 2 times 10 times 5 = 100 J. On falling, all of it becomes kinetic energy, 100 J; from half m v squared equals 100, v squared = 100 so v = 4 m/s.

Heat Transfer and Specific Heat Capacity

These questions cover specific heat capacity, mixture temperature, heater power and methods of heat transfer. Take the specific heat capacity of water as 4200 J/(kg C).

#	Question	Answer and marking notes
21	A mass of 0.5 kg of water is heated so that its temperature rises by 20 degrees C. Find the heat absorbed.	Answer: Q = mc times delta T = 0.5 times 4200 times 20 = 42000 J. A larger specific heat capacity means more heat is needed for the same rise in temperature, which is why water is a good coolant.
22	Masses of 200 g of water at 80 degrees C and 300 g at 20 degrees C are mixed with no heat loss. Find the final temperature.	Answer: let the final temperature be T; heat lost by the hot water equals heat gained by the cold water. T = (200 times 80 plus 300 times 20) divided by 500 = 22000 divided by 500 = 44 degrees C. The answer must lie between 20 and 80 degrees C, a useful check.
23	A kettle supplies the heat in part 1 in 100 s. Find its average power and say whether its real rating would be higher or lower.	Answer: P = Q divided by t = 42000 divided by 100 = 420 W. The real rating must be higher, because some heat escapes to the surrounding air and the body of the kettle, so efficiency cannot reach 100 percent.
24	Explain the mechanisms of conduction, convection and radiation with one everyday example each, and why a vacuum flask reduces all three at once.	Answer: conduction transfers heat by particle collisions without bulk flow, for example a metal spoon warming in hot soup. Convection arises when a heated fluid expands, becomes less dense and rises, setting up a circulation, as when an air conditioner mounted high mixes a room. Radiation carries heat as electromagnetic waves and needs no medium, as when you feel warmth in sunlight. A vacuum flask has a vacuum between its double walls, removing the medium for conduction and convection, silvered inner walls that reflect radiation, and a stopper that limits convection at the top.

Find a tutor — free Tutor Registration →

A TutorZone practice paper; original questions and passages, not publisher material.