Physics

What is the unit of force?

• AWatt
• BPascal
• CNewton✓
• DJoule

Answer: Force is measured in newtons (N). 1 N is the force that accelerates 1 kg by 1 m/s².

Which equation correctly links speed, distance and time?

• Aspeed = distance ÷ time✓
• Bspeed = distance × time
• Cspeed = distance + time
• Dspeed = time ÷ distance

Answer: Speed = distance ÷ time (v = s ÷ t).

What is the resultant force on an object moving at constant velocity?

• AZero✓
• BIncreasing
• CEqual to its weight
• DEqual to its mass

Answer: At constant velocity the forces are balanced, so the resultant (net) force is zero (Newton's first law).

Which of these is the correct equation for weight?

• AW = m ÷ g
• BW = m + g
• CW = m × g✓
• DW = g ÷ m

Answer: Weight = mass × gravitational field strength (W = m g). On Earth g ≈ 9.8 N/kg.

Energy cannot be created or destroyed, only transferred or stored. This is the principle of:

• AConservation of momentum
• BConservation of energy✓
• COhm's law
• DNewton's third law

Answer: The conservation of energy principle states energy is conserved — it changes store/form but the total stays the same.

What is the unit of electrical resistance?

• AAmpere
• BVolt
• CWatt
• DOhm✓

Answer: Resistance is measured in ohms (Ω). V = I × R links voltage, current and resistance.

In a series circuit, the current is:

• AThe same at all points✓
• BAlways increasing
• CDifferent at each component
• DZero

Answer: In a series circuit there is only one path, so the current is the same everywhere.

Which type of radiation is the most penetrating?

• AAlpha
• BBeta
• CThey are equal
• DGamma✓

Answer: Gamma radiation is the most penetrating (stopped only by thick lead/concrete); alpha is the least.

What energy transfer happens in a filament lamp?

• ALight to electrical
• BChemical to kinetic
• CElectrical to light (and heat)✓
• DSound to electrical

Answer: A lamp transfers electrical energy mainly to light, with some wasted as heat (thermal) energy.

The frequency of a wave is measured in:

• AMetres
• BSeconds
• CHertz✓
• DNewtons

Answer: Frequency is the number of waves per second, measured in hertz (Hz).

Which equation gives the wave speed?

• Aspeed = wavelength ÷ frequency
• Bspeed = frequency ÷ wavelength
• Cspeed = frequency × wavelength✓
• Dspeed = frequency + wavelength

Answer: Wave speed = frequency × wavelength (v = f λ).

Sound waves are an example of which type of wave?

• AElectromagnetic
• BTransverse
• CLongitudinal✓
• DStanding only

Answer: Sound is a longitudinal wave: the particles vibrate parallel to the direction of energy transfer.

What happens to the particles in a substance as it is heated?

• AThey gain kinetic energy and move/vibrate faster✓
• BThey lose energy and slow down
• CThey become heavier
• DThey disappear

Answer: Heating transfers energy to the particles, increasing their kinetic energy so they move or vibrate faster. During a change of state the energy goes into breaking the forces between particles instead, so the temperature stays the same.

Which of these is a renewable energy resource?

• AWind✓
• BNatural gas
• CCoal
• DOil

Answer: Wind is renewable (it won't run out). Coal, gas and oil are finite fossil fuels.

Newton's third law states that every action has an equal and opposite:

• AMomentum
• BAcceleration
• CVelocity
• DReaction✓

Answer: Newton's third law: for every action force there is an equal and opposite reaction force.

A distance–time graph for a walker has three stages: 400 m covered in the first 100 s, then a flat section lasting 50 s while the walker rests, then a further 200 m covered in the next 50 s. What is the average speed for the whole journey?

• A6 m/s
• B4 m/s
• C3 m/s✓
• D2 m/s

Answer: Average speed uses the totals for the whole journey. Total distance = 400 m + 200 m = 600 m and total time = 100 s + 50 s + 50 s = 200 s, so average speed = 600 ÷ 200 = 3 m/s. Leaving the resting time out of the total time gives 4 m/s, and a flat section on a distance–time graph means the walker is stationary.

A train speeds up steadily from 8 m/s to 32 m/s in 12 seconds. What is its acceleration?

• A2 m/s²✓
• B2.67 m/s²
• C44 m/s²
• D288 m/s²

Answer: Acceleration = change in velocity ÷ time taken = (32 − 8) ÷ 12 = 24 ÷ 12 = 2 m/s². Using the final velocity without subtracting the starting velocity gives 2.67 m/s², and multiplying the change in velocity by the time gives 288 m/s².

A car has a mass of 900 kg and accelerates at 2.5 m/s². What is the resultant force acting on the car?

• A0.0028 N
• B360 N
• C902.5 N
• D2250 N✓

Answer: Force = mass × acceleration = 900 kg × 2.5 m/s² = 2250 N. Dividing the mass by the acceleration gives 360 N, dividing the acceleration by the mass gives 0.0028 N, and adding the two values gives 902.5 N.

A crate of mass 30 kg is lifted 4.0 m at a steady speed. Take the gravitational field strength to be g = 10 N/kg. How much work is done against gravity?

• A40 J
• B120 J
• C300 J
• D1200 J✓

Answer: Weight = mass × gravitational field strength = 30 kg × 10 N/kg = 300 N. Work done = force × distance = 300 N × 4.0 m = 1200 J, which is also the gravitational potential energy the crate gains. Leaving g out of the working gives 120 J, and stopping at the weight gives 300 N rather than an energy.

A cyclist and bicycle have a combined mass of 60 kg and are moving at 10 m/s. What is their kinetic energy?

• A300 J
• B600 J
• C3000 J✓
• D6000 J

Answer: Kinetic energy = ½ × mass × velocity² = 0.5 × 60 × 10² = 0.5 × 60 × 100 = 3000 J. Forgetting to square the velocity gives 300 J, and leaving out the ½ gives 6000 J.

An electric motor is supplied with 1200 J of energy. It transfers 300 J usefully and wastes the other 900 J by heating. What is the efficiency of the motor as a percentage?

• A25%✓
• B33%
• C75%
• D400%

Answer: Efficiency = useful energy transferred ÷ total energy supplied × 100 = 300 ÷ 1200 × 100 = 25%. Dividing the useful energy by the wasted energy gives 33%, and 75% is the percentage that is wasted rather than the percentage that is useful.

A lamp has a total power input of 60 W and a useful light output of 9 W. What is the efficiency of the lamp, given as a decimal?

• A0.15✓
• B0.85
• C1.5
• D6.7

Answer: Efficiency = useful power output ÷ total power input = 9 ÷ 60 = 0.15. Written as a decimal, efficiency can never be greater than 1, so turning the division upside down to get 6.7 cannot be right. The figure 0.85 is the fraction of the power that is wasted.

A student finds the mass of a metal block to be 240 g and uses a displacement can to measure its volume as 30 cm³. What is the density of the metal?

• A0.125 g/cm³
• B8 g/cm³✓
• C210 g/cm³
• D7200 g/cm³

Answer: Density = mass ÷ volume = 240 g ÷ 30 cm³ = 8 g/cm³. Dividing the volume by the mass gives 0.125 g/cm³, multiplying them gives 7200 g/cm³, and subtracting gives 210.

A sound wave has a frequency of 170 Hz and a wavelength of 2.0 m. What is the speed of the wave?

• A0.012 m/s
• B85 m/s
• C172 m/s
• D340 m/s✓

Answer: Wave speed = frequency × wavelength = 170 Hz × 2.0 m = 340 m/s, which is about the speed of sound in air. Dividing the frequency by the wavelength gives 85 m/s and adding the two values gives 172 m/s.

A trolley of mass 2.0 kg moving at 3.0 m/s collides with a stationary trolley of mass 4.0 kg. The trolleys join together and move off as one. Momentum is conserved. What is their speed immediately after the collision?

• A0.5 m/s
• B1.0 m/s✓
• C1.5 m/s
• D3.0 m/s

Answer: Momentum before = mass × velocity = 2.0 kg × 3.0 m/s = 6.0 kg m/s; the stationary trolley contributes none. After the collision the moving mass is 2.0 + 4.0 = 6.0 kg, so speed = 6.0 ÷ 6.0 = 1.0 m/s. Dividing the momentum by the stationary trolley's mass alone gives 1.5 m/s.

A radioactive source has an activity of 800 Bq and a half-life of 6 hours. What will its activity be after 24 hours?

• A50 Bq✓
• B100 Bq
• C200 Bq
• D400 Bq

Answer: 24 hours ÷ 6 hours = 4 half-lives. The activity halves once for each of them: 800 → 400 → 200 → 100 → 50 Bq. Halving only three times gives 100 Bq, and the activity is halved rather than reduced by a fixed amount each time.

A car is travelling at 20 m/s. The driver's reaction time is 0.7 s and the braking distance is 26 m. What is the total stopping distance?

• A14 m
• B20 m
• C26 m
• D40 m✓

Answer: Thinking distance = speed × reaction time = 20 m/s × 0.7 s = 14 m. Stopping distance = thinking distance + braking distance = 14 m + 26 m = 40 m. Quoting only the braking distance gives 26 m and quoting only the thinking distance gives 14 m.

A 2.0 kg block of aluminium is heated from 20°C to 45°C. The specific heat capacity of aluminium is 900 J/kg°C. How much energy is transferred to the block?

• A1800 J
• B45 000 J✓
• C36 000 J
• D81 000 J

Answer: Energy transferred = mass × specific heat capacity × temperature change. The temperature change is 45 − 20 = 25°C, so the energy is 2.0 × 900 × 25 = 45 000 J. Using the final temperature of 45°C in place of the rise gives 81 000 J, and leaving the temperature change out altogether gives 1800 J.

A heater with a resistance of 46 Ω is connected to the 230 V mains supply. What is the power of the heater?

• A5 W
• B46 W
• C1150 W✓
• D10 580 W

Answer: First find the current: I = V ÷ R = 230 ÷ 46 = 5 A. Then power = potential difference × current = 230 V × 5 A = 1150 W. Stopping at the current gives 5, which is an ampere value and not a power, and multiplying the potential difference by the resistance instead of dividing gives a figure more than nine times too big.

An immersion heater has an element of resistance 20 Ω and draws a current of 10 A. It is switched on for 30 minutes. Electricity costs 30p per kWh. What does it cost to run the heater?

• A£0.03
• B£0.30✓
• C£0.60
• D£18.00

Answer: Power = current² × resistance = 10² × 20 = 100 × 20 = 2000 W, which is 2 kW. Energy transferred = power × time = 2 kW × 0.5 hours = 1 kWh. Cost = 1 × 30p = £0.30. Forgetting to square the current gives a power of 200 W and a cost of £0.03. The 30 minutes must be converted into 0.5 hours; using 30 hours instead gives £18.00.