Motion and forces - Six-mark questions

Six-mark questions are often the questions that people find the most difficult. In all longer answer questions, but especially the six-mark ones, it is important that you plan your answer and not just rush into it. After all, you would plan an essay or short story before starting. Without a plan it is easy to stray away from the key point and lose marks, get steps in a process in the wrong order or forget key bits of information.

Six-mark questions will start with command words such as 'describe' or 'explain'. The command words 'describe' and 'explain' can be confusing. If you are asked to describe a graph, you will be expected to write about its overall shape, whether it is linear or curved, the slope of gradients etc. If you are asked to explain why a pattern or trend is seen in a graph, you will be expected to use your science knowledge, not just say what you see (which is a description), eg 'The graph shows the number of radioactive nuclei decreases as time increases. It does this because…'

'Explain how' and 'why' questions often have the word 'because' in their answer. 'Describe' questions don't.

The number of marks per question part is given in the form '[6 marks]'. It is essential that you give as many different points in your answer as possible, linking these together. Often, you will be asked to compare two things: make sure that you include both in your answer otherwise, you are likely to limit your score to two marks out of six marks.

Edexcel questions courtesy of Pearson Education Ltd.

Sample question 1 - Foundation and Higher

Question

The graph below shows the thinking, braking and stopping distances for an average car and driver stopping from 50 miles per hour as shown in the Highway Code. It also shows the thinking, braking and stopping distances for drivers of cars A and B, both stopping from 50 miles per hour:

A bar chart shows the thinking and braking distance of the Highway Code and two cars.

A and B are different cars on different roads.

Use the factors that can affect thinking and braking distances to explain the differences in stopping distances for cars A and B. [6 marks]

  • The stopping distance is the sum of the thinking distance and braking distance. [1]
  • The thinking distance is affected by whether the driver is tired or under the influence of drugs or alcohol. [1]
  • The braking distances depends on the condition of the car - for example whether the brakes are in good condition and there is tread on the tyres. [1]
  • Braking distance is also affected by the mass of the car or load being carried, the road surface, whether it is wet or icy and whether the car is travelling up hill or down hill. [1]
  • Car A has a thinking distance of 22 m which is longer than the average driver in the Highway Code so car A might have a drunk driver. [1]
  • Car B had a longer braking distance (71 - 12 = 59 m) than the average driver so car B might be on a wet road. [1]

Plan the key points that you should include in your answer. Begin by explaining what is meant by stopping distance. Then consider factors that affect the thinking distance and braking distance. You should try to use data from the chart in your suggestion of why the stopping distances are different.

Sample question 2 - Higher

Question

A model rocket contains 50 g of fuel when it takes off. The fuel burns and the model rocket rises vertically. After a while, there is no fuel left. Eventually the empty model rocket falls back to the ground.

The graph is a velocity-time graph for the model rocket. Four stages are labelled on the graph.

This graph shows the velocity against time for a toy rocket taking off, running out of fuel and falling back to the ground.

Explain why the velocity of the model rocket changes as shown in the graph. [6 marks]

  • In stage 1 the model rocket accelerates upwards as fuel is being burnt, because the thrust force upwards is greater than the weight [1].
  • In stage 2 the model rocket decelerates (accelerates downwards) because it has run out of fuel [1]. The slope of the graph is constant because the weight is constant [1].
  • In stage 3 the model rocket is continuing to accelerate downwards but the velocity is now negative because the model rocket is now falling [1].
  • Finally in stage 4 the model rocket comes to rest [1]. There is a rapid deceleration and large resultant force as it hits the ground [1].

Plan the key points that you should include in your answer. For each stage of the graph you should describe the shape, explain the reason for the shape and finally link this to an explanation for the change in velocity.