Forces — OCR GCSE Physics
In summary: Forces is a key topic in OCR GCSE Physics. Key exam tip: Always check if a question asks for speed (scalar) or velocity (vector).
Exam Tips for Forces
- Always check if a question asks for speed (scalar) or velocity (vector).
- When interpreting graphs, look closely at the axes labels to determine if it is a distance-time or velocity-time graph.
- Show all working out for calculations, including the formula used and unit conversions.
- Remember that the area under a velocity-time graph represents displacement.
- Be prepared to use the equation v^2 - u^2 = 2as for problems involving acceleration where time is not given.
- Always draw free body diagrams to visualize forces acting on an object
- Ensure you can distinguish between scalar and vector quantities clearly
- Practice resolving forces using scale drawings for parallel and perpendicular vectors
Common Mistakes
- Confusing scalar and vector quantities.
- Assuming velocity must always be positive.
- Failing to associate a change in direction with a change in sign for vector quantities.
- Misinterpreting the slope of a distance-time graph as velocity and a velocity-time graph as acceleration.
- Incorrectly calculating the area under a velocity-time graph when the motion is complex.
- Believing that a net force is required for an object to continue moving steadily
Marking Points
- Correct distinction between scalar and vector quantities (e.g., speed vs velocity, distance vs displacement).
- Accurate interpretation of slopes on distance-time and velocity-time graphs.
- Correct calculation of area under a velocity-time graph to determine displacement.
- Correct application of the equation v^2 - u^2 = 2as for uniform acceleration.
- Correct use of units (m, s, m/s, m/s^2) in all calculations.
- Correct calculation of average speed for non-uniform motion.
- Identification of contact and non-contact forces
- Application of Newton’s first law to objects with uniform velocity or changing motion
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