Velocity In Rolling Motion
A wheel of radius 0.4 m rolls without slipping along a level road while the speed of its centre is 5 m/s. What is the instantaneous speed of the topmost point on the rim of the wheel?
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Solution
10m/s
In rolling without slipping, the contact point with the ground is instantaneously at rest, and every other point's velocity is the vector sum of the centre's translation v and the rotation ωr about the centre. The no-slip condition fixes ω=v/R, so the rim speed relative to the centre equals v itself. At the topmost point the translational velocity v and the rotational velocity ωR=v point in the same forward direction and therefore add: vtop=v+v=2v=2×5=10 m/s. The value 5 m/s gives only the centre's speed and ignores the rotational contribution. The value 0 m/s describes the bottom contact point, not the top. The value 7.5 m/s uses an incorrect intermediate factor of 1.5. This is the NCERT velocity analysis of a rolling wheel. As a check, the top must be the fastest point of the wheel, exceeding the centre's 5 m/s, and 10 m/s correctly captures that maximum. More generally, every point on the rim traces a cycloidal path as the wheel advances, with its speed ranging from zero at the ground contact to twice the hub speed at the very top, while a point level with the axle moves at 2v.
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About This Question
- Subject
- physics
- Chapter
- rotational motion
- Topic
- velocity in rolling motion
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
10m/s
In rolling without slipping, the contact point with the ground is instantaneously at rest, and every other point's velocity is the vector sum of the centre's translation v and the rotation ωr about the centre. The no-slip condition fixes ω=v/R, so the rim speed relative to the centre equals v itself. At the topmost point the translational velocity v and the rotational velocity ωR=v point in the same forward direction and therefore add: vtop=v+v=2v=2×5=10 m/s. The value 5 m/s gives only the centre's speed and ignores the rotational contribution. The value 0 m/s describes the bottom contact point, not the top. The value 7.5 m/s uses an incorrect intermediate factor of 1.5. This is the NCERT velocity analysis of a rolling wheel. As a check, the top must be the fastest point of the wheel, exceeding the centre's 5 m/s, and 10 m/s correctly captures that maximum. More generally, every point on the rim traces a cycloidal path as the wheel advances, with its speed ranging from zero at the ground contact to twice the hub speed at the very top, while a point level with the axle moves at 2v.
This medium difficulty physics question is from the chapter rotational motion, covering the topic of velocity in rolling motion. It appeared in the 2025 exam.
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