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NEET PHYSICSMOTION IN A PLANEMedium

Question

Two particles AA and BB, move with constant velocities v1\vec{v}_1 and v2\vec{v}_2 respectively. At the initial moment, their position vectors are r1\vec{r}_1 and r2\vec{r}_2 respectively. The condition for particles AA and BB for their collision will be:

A

r1r2r1r2=v2v1v2v1\frac{\vec{r}_1 - \vec{r}_2}{|\vec{r}_1 - \vec{r}_2|} = \frac{\vec{v}_2 - \vec{v}_1}{|\vec{v}_2 - \vec{v}_1|}

B

r1v1=r2v2\vec{r}_1 \cdot \vec{v}_1 = \vec{r}_2 \cdot \vec{v}_2

C

r1×v1=r2×v2\vec{r}_1 \times \vec{v}_1 = \vec{r}_2 \times \vec{v}_2

D

r1r2=v1v2\vec{r}_1 - \vec{r}_2 = \vec{v}_1 - \vec{v}_2

Step-by-Step Solution

  1. Condition for Collision: For two particles to collide, they must occupy the same position at the same instant of time tt (t>0t > 0).
  2. Position Equations:
  • Position of particle A at time tt: rA(t)=r1+v1t\vec{r}_A(t) = \vec{r}_1 + \vec{v}_1 t
  • Position of particle B at time tt: rB(t)=r2+v2t\vec{r}_B(t) = \vec{r}_2 + \vec{v}_2 t
  1. Equating Positions: r1+v1t=r2+v2t\vec{r}_1 + \vec{v}_1 t = \vec{r}_2 + \vec{v}_2 t r1r2=(v2v1)t\vec{r}_1 - \vec{r}_2 = (\vec{v}_2 - \vec{v}_1) t
  2. Direction Analysis: The equation implies that the relative displacement vector (r1r2)(\vec{r}_1 - \vec{r}_2) is parallel to the relative velocity vector (v2v1)(\vec{v}_2 - \vec{v}_1). Since time tt must be positive for a future collision, these two vectors must point in the same direction.
  3. Unit Vectors: If two vectors are in the same direction, their unit vectors must be equal . r^relative=v^relative\hat{r}_{relative} = \hat{v}_{relative} r1r2r1r2=v2v1v2v1\frac{\vec{r}_1 - \vec{r}_2}{|\vec{r}_1 - \vec{r}_2|} = \frac{\vec{v}_2 - \vec{v}_1}{|\vec{v}_2 - \vec{v}_1|}

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from MOTION IN A PLANE. 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.

PHYSICSMOTION IN A PLANEparticlesconstantvelocitiesrespectivelyinitial

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