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NEET PHYSICSRotational motionMedium

Question

If F\vec{F} is the force acting on a particle having position vector r\vec{r} and τ\vec{\tau} be the torque of this force about the origin, then:

A

rτ0\vec{r} \cdot \vec{\tau} \neq 0 and Fτ=0\vec{F} \cdot \vec{\tau} = 0

B

rτ>0\vec{r} \cdot \vec{\tau} > 0 and Fτ<0\vec{F} \cdot \vec{\tau} < 0

C

rτ=0\vec{r} \cdot \vec{\tau} = 0 and Fτ=0\vec{F} \cdot \vec{\tau} = 0

D

rτ=0\vec{r} \cdot \vec{\tau} = 0 and Fτ0\vec{F} \cdot \vec{\tau} \neq 0

Step-by-Step Solution

Torque is mathematically defined as the cross product of the position vector (r\vec{r}) and the force vector (F\vec{F}), i.e., τ=r×F\vec{\tau} = \vec{r} \times \vec{F}. A fundamental property of the cross product is that the resulting vector (τ\vec{\tau}) is always perpendicular (orthogonal) to the plane containing both r\vec{r} and F\vec{F}. Consequently, τ\vec{\tau} is perpendicular to r\vec{r} and also perpendicular to F\vec{F}. Since the dot product of any two perpendicular vectors is zero, we must have rτ=0\vec{r} \cdot \vec{\tau} = 0 and Fτ=0\vec{F} \cdot \vec{\tau} = 0.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from Rotational motion. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSRotational motionactingparticlehavingpositionvector

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