IB · A · extended response
A safer catch with the same momentum change
Space, time and motion · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- discriminating
- Marks
- 6
- Topics
- 1
- Answer
- Complete
Stopping-force magnitude: design A
Supplied question data. Read the labelled axes and use the observations to test the physical model.
Vertical axis (y): Force magnitude / N
Horizontal axis (x): Time / s
Read the exact data as a table
| Time / s | Force magnitude / N |
|---|---|
| 0 | 0 |
| 0.01 | 300 |
| 0.02 | 0 |
These are the supplied values, not a worked answer. Lines join the supplied values; they are not a fitted model.
A 0.20 kg ball arrives horizontally at 15 m s⁻¹ and is brought to rest. Design A produces the triangular stopping-force magnitude shown below. Design B gives the same impulse with a triangular pulse lasting 0.060 s. Ignore gravity during the short horizontal catch. Supplied data (Time / s; Force magnitude / N): (0, 0), (0.01, 300), (0.02, 0).
- (a)
Check design A's impulse and find its average force. Determine the peak force needed for design B.
3 marks - (b)
Evaluate the claim that extending the catch reduces the impulse and the energy absorbed.
3 marks
Ready to self-mark?Reveal the detailed answer guide
(a)
Check design A's impulse and find its average force. Determine the peak force needed for design B.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
The required momentum-change magnitude is mΔv = 0.20(15) = 3.0 kg m s⁻¹, opposite the initial motion.
- 2
The triangle area is ½(0.020)(300) = 3.0 N s, consistent with stopping. Average force is 3.0/0.020 = 150 N.
- 3
For design B, ½(0.060)Fpeak = 3.0, giving 100 N. The average is 50 N, half the peak for a triangular pulse.
(b)
Evaluate the claim that extending the catch reduces the impulse and the energy absorbed.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
The ball has the same initial and final momentum, so its impulse cannot change merely by spreading the catch over time.
- 2
Its kinetic-energy reduction is ½(0.20)(15²) = 22.5 J in both cases. The longer catch can distribute that transfer over a larger distance.
- 3
Lower peak force can reduce injury or damage, but actual safety also depends on pressure, contact area, material deformation and the available stopping distance.
Complete marking guidance
Use these worked steps alongside the part-by-part answers. They explain the method and mark allocation; they do not add extra marks.
- The required momentum-change magnitude is mΔv = 0.20(15) = 3.0 kg m s⁻¹, opposite the initial motion.
- The triangle area is ½(0.020)(300) = 3.0 N s, consistent with stopping. Average force is 3.0/0.020 = 150 N.
- For design B, ½(0.060)Fpeak = 3.0, giving 100 N. The average is 50 N, half the peak for a triangular pulse.
- The ball has the same initial and final momentum, so its impulse cannot change merely by spreading the catch over time.
- Its kinetic-energy reduction is ½(0.20)(15²) = 22.5 J in both cases. The longer catch can distribute that transfer over a larger distance.
- Lower peak force can reduce injury or damage, but actual safety also depends on pressure, contact area, material deformation and the available stopping distance.
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