Edexcel A-Level Physics 9PH0
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Further Mechanics
Investigating momentum and analysing collisions on video
- 1 thing to know
- Papers 1 and 3
Overview
Recall questions on the core practical linking force to change of momentum, the graph and its gradient, the systematic error, and video analysis of colliding spheres.
What you need to know
Answer each one before you reveal it.
Questions from this subtopic
Each one with the model answer underneath.
- 1
In the core practical linking force to change of momentum, how is a steady accelerating force applied to a trolley?
Model answer
A hanging mass on a string passing over a pulley at the end of the runway provides a constant pulling force on the trolley.
- 2
In that practical, how is the trolley's change of momentum measured?
Model answer
Its velocity is measured using light gates with an interrupt card, or a motion sensor, and the change of momentum is the trolley's mass multiplied by its change of velocity.
- 3
In the core practical linking force to change of momentum, what graph would you produce, and what should its gradient equal?
Model answer
Plotting change of momentum against the time for which the force acted should give a straight line through the origin whose gradient is the accelerating force.
- 4
In the core practical linking force to change of momentum, what systematic error affects the results, and how can it be reduced?
Model answer
Friction in the wheels and pulley makes the measured momentum change too small; it is reduced by tilting the runway slightly so the trolley moves at constant velocity when given a gentle push.
- 5
How is ICT used to analyse a collision between small spheres such as ball bearings on a table top?
Model answer
The collision is filmed at a high frame rate and video-analysis software tracks the position of each sphere frame by frame, so velocity components before and after can be calculated from the known time between frames.
- 6
Why must a metre rule or similar scale appear in the video frame during that analysis?
Model answer
It calibrates the recording, allowing distances measured on screen in pixels to be converted into real distances in the plane of motion.
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