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# Velocity and acceleration vector of a charged particle moving in a magnetic field at some instant are $\overrightarrow V = 3\hat i + 4\hat j\: and\: \overrightarrow B= 2\hat i + x \hat j$. Select the incorrect alternative

$\begin {array} {1 1} (a)\;X = 3 & \quad (b)\;The\: particle\: follows\: a \: circular \: path \\ (c)\;Magnetic\: field \: is\: along\: the\: z - direction & \quad (d)\;Kinetic \: energy \: of \: the \: particle\: is \: constant \end {array}$

Magnetic force is always $\perp$ to the velocity. This gives $x = -1.5$
Field is $\perp$ to the plain of the velocity($x-y$ plane)
Magnetic field does no work ($KE$ is constant)
Ans : (a)