# Explaining motion - Six-mark questions

Six-mark questions will only appear in the Depth paper. There will be two six-mark questions in the Depth paper.

Six-mark questions are extended free-response questions, requiring the longest answers. It is wise to plan your answer rather than rushing straight into it. 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.

To gain six marks, you will need to:

• use appropriate scientific words and terms
• write clearly, linking ideas in a logical way
• maintain a sustained line of reasoning, rather than a random list of statements and sentences
• support explanations using scientific knowledge and understanding

Six-mark questions are marked using a levels-based mark scheme. An answer that is not clear and logically sequenced, and which does not give a coherent argument supported by evidence, will be limited to the lower levels. Similarly, if the question asks you to discuss both sides of an argument, or explain two observations, you will be limited to the lowest level if your answer only considers one of them (no matter how brilliantly written or comprehensively explained that one is!).

## Sample question 1 - Foundation

Question

This question is about the forces that make a car move forwards.

The rotation of a wheel causes the car to move forward.

When the road is icy, it is more difficult to get the car moving.

Use ideas about forces to explain how the rotation of a wheel makes the car move forward and why it is more difficult to get the car moving when the road is icy.

OCR 21st Century Science, GCE Physics, Paper A182, June 2015.

The rotating wheel pushes the road in a backwards direction, and the road pushes back on the wheel in the forward direction [1] - this is the force pair and the resultant force moves the car forward [1]. In normal driving conditions there is friction between the wheel and the road [1] - the wheel grips the road and a force is exerted [1]. When the road is icy there is little or no friction between the wheel and the road [1] - this means there is less grip and the force exerted is a lot less [1].

To get into the five to six mark band for this question there needs to be a well-developed line of reasoning and your answer needs to be clear and logically structured. A good idea is to plan your response before writing it. Write down the force pair that makes the car move and the effect of an icy road vs a normal road when it comes to driving. When writing your answer, write in clear concise language and full sentences. You should give details of both normal and icy roads and mention the forces that are between the wheel and the road.

## Sample question 2 - Foundation

Question

A simple roller coaster has one line of track on which a vehicle travels backwards and forwards.

• the vehicle is pulled up the left side of the track, and is then released
• it travels down the track, speeding up as it moves
• it rises up the right side of the track, slowing down as it moves upwards
• it rolls back down
• it moves backwards and forwards on the track several times, with each move becoming lower and lower and the top speed becoming slower and slower

Use ideas of energy to explain the motion of the vehicle. [6 marks]

OCR 21st Century Science, GCE Physics, Paper A182, June 2015.

As the vehicle moves up the ramp it gains gravitational potential energy. This turns into kinetic energy as it falls [1]. As it descends the ramp, kinetic energy increases, meaning the speed increases [1]. As it ascends the other side, kinetic energy decreases and GPE increases so the speed decreases [1]. In each movement, energy is dissipated to the surroundings as heat, due to the friction between the wheels and the surface of the ramp. This means that with each movement, the speed and height of rise decreases [1]. After the initial energy input, there is no more energy added, so over time the speed and height will keep reducing until the vehicle no longer moves and all energy is dissipated as heat to the surroundings [1]. Due to the total energy being conserved, we know that the initial amount of energy will equal the amount transferred as heat [1].

It is important to consider the law of conservation of energy in your answer. Discuss how the energy is stored and transferred, relating it to the motion of the vehicle. Explain why the speed and height of the vehicle decreases over time, making sure you mention where this energy is going. Remember the energy is not lost - it is merely transferred to the surroundings as heat caused by friction (and potentially some sound).