Q 11-03-008NEETJEE MainEAMCET 2007 (Engineering)Easy
Velocity and acceleration vectors of a charged particle moving perpendicular to the direction of a magnetic field at a given instant of time are $\vec{v} = 2\hat{i} + c\hat{j}$ and $\vec{a} = 3\hat{i} + 4\hat{j}$ respectively. Then the value of $c$ is
Answer: (C) $-1.5$
Concept. The magnetic force $q\vec v \times \vec B$ is perpendicular to $\vec v$, so $\vec v \cdot \vec a = 0$.
Step 1. Dot product. $2(3) + c(4) = 0 \Rightarrow c = -1.5$.
Answer. $-1.5$ (Option C).
Solution by Sreeraj P, M.Sc Physics