AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2023: Question 2

Trolley Acceleration and Resultant Force

Topics covered

• Required practical style method planning
• Newton’s laws of motion
• Force, mass and acceleration
• Using data and equations accurately

What examiners were looking for

Clear, logical answers. For the method question, the best responses included how to change the force, what to measure, what equipment to use, and how to repeat the test fairly. For the calculations, examiners wanted correct use of proportionality or F = ma, with units.

✅ Correct answer

A full-mark method needs to be logical and detailed. One valid method is:

1. Clamp a pulley to the edge of the bench.
2. Attach a string to the trolley and pass the string over the pulley.
3. Attach a mass holder to the end of the string.
4. Add a slotted mass to the mass holder to provide a pulling force.
5. Mark a start point and finish point on the runway and measure the distance between them using a metre rule.
6. Release the trolley from the same starting point each time.
7. Measure the time taken for the trolley to travel between the two marks using a stopwatch or timer.
8. Use W = mg to calculate the force provided by the hanging mass.
9. Calculate the acceleration of the trolley. You could use speed and change in speed, or use light gates/computer equipment to calculate acceleration directly.
10. Repeat with different numbers of slotted masses to change the force.
11. Repeat each force more than once and calculate a mean.
12. Keep other variables the same, especially the same trolley and same runway setup.

💡 Key knowledge

• The force can be varied by changing the hanging mass on a string over a pulley.
• The force from the hanging mass is its weight: W = mg .
• Acceleration can be found from timing measurements, or more accurately using light gates.
• You must describe extra equipment, not just say “measure it”.
• The mark scheme also allowed another valid method: changing the height of the runway using wooden blocks.

🧠 Exam technique

• Use a clear sequence: set up → vary force → measure → calculate → repeat.
• Name the extra equipment: pulley, string, mass holder, slotted masses, metre rule, stopwatch or light gates.
• Explain how the force is known: calculate it from the weight of the hanging mass.
• Include repeats for reliability.
• Top-level answers link each step to the aim of the investigation.

❌ Common errors

• Only saying “add more force” without explaining how.
• Not naming any extra equipment.
• Describing speed instead of acceleration without explaining how acceleration is found.
• Missing repeats.
• Giving steps in a muddled order, so the method would not clearly work.

Examiner insight: Students lost marks when they gave a vague practical plan. The strongest answers were specific and logically sequenced.

✅ Correct answer

Newton’s second law

💡 Key knowledge

Newton’s second law shows that resultant force, mass and acceleration are linked: F = ma . For a constant mass, acceleration is directly proportional to resultant force.

❌ Common errors

• Choosing the first law because it also mentions forces and motion.
• Choosing the third law because students remember “action and reaction” but it does not link force to acceleration in this way.

✅ Correct answer

From the table:

1.2 N → 1.6 m/s²

If the force becomes 3.6 N , that is 3.6 ÷ 1.2 = 3 times bigger.

So the acceleration is also 3 times bigger:

1.6 × 3 = 4.8 m/s²

Acceleration = 4.8 m/s²

📐 Calculations

1. Find how many times the force has increased:
   3.6 ÷ 1.2 = 3
2. Multiply the original acceleration by 3:
   1.6 × 3 = 4.8
3. Write the unit:
   m/s²

Alternative method from the mark scheme:

m = 1.2 ÷ 1.6 = 0.75 kg , then a = 3.6 ÷ 0.75 = 4.8 m/s²

🧠 Exam technique

Because the question says “Use Table 1”, the fastest method is proportional reasoning. This saves time and is exactly what the examiner expects.

❌ Common errors

• Adding instead of multiplying.
• Using the ratio upside down.
• Forgetting the unit m/s² .
• Assuming the mass changes when the question gives no sign of that.

✅ Correct answer

F = ma

or

resultant force = mass × acceleration

💡 Key knowledge

• F is resultant force in newtons, N
• m is mass in kilograms, kg
• a is acceleration in metres per second squared, m/s²

❌ Common errors

• Writing F = mv
• Writing weight equations such as W = mg instead
• Missing out that the force is the resultant force

✅ Correct answer

Use F = ma

Substitute the values:

0.42 = m × 1.2

Rearrange:

m = 0.42 ÷ 1.2

m = 0.35 kg

Mass of trolley = 0.35 kg

📐 Calculations

1. Write the equation:
   F = ma
2. Rearrange for mass:
   m = F ÷ a
3. Substitute the numbers:
   m = 0.42 ÷ 1.2
4. Calculate:
   m = 0.35
5. Add the correct unit:
   kg

🧠 Exam technique

• Always rearrange the equation before substituting if it helps avoid mistakes.
• Show each line clearly to pick up method marks even if your final answer is wrong.
• Check whether the unit should be kg, not g.

❌ Common errors

• Doing 1.2 ÷ 0.42 instead of 0.42 ÷ 1.2
• Multiplying instead of dividing.
• Forgetting the unit kg .
• Using weight equation W = mg instead of F = ma .

💡 Must-know facts

• Acceleration is proportional to resultant force if mass stays constant.
• This is Newton’s second law.
• F = ma is one of the most important equations in forces.

🧠 How to score highly

• For method questions, be specific and ordered.
• For data questions, look for simple ratios first.
• For calculations, write the equation, substitute, calculate, then give units.

❌ Biggest traps in this question

• Vague practical descriptions.
• Confusing Newton’s laws.
• Not using proportionality in part 02.3.
• Dropping units in numerical answers.