How does magnetic force only affect direction of velocity and not kinetic energy? As kinetic energy = 1/2 MVsquare and depends on velocity.

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Solution

Magnetic force is always perpendicular to velocity, since it causes circular motion. magnetic force can cause a charged particle to move in a circular or spiral path. the particles kinetic energy and speed thus remains constant. the direction of motion is affected but not the speed. this is typical of uniform circular motion. here the magneticforce suppfor motion parallel to the field.lies the centripetal force Fc=mv2/r noting sinθ=1.the magnetic force is perpendicular to the velocity and so velocity changes in direction but not magnitde.
. if the velocity is not perpendicular to the magnetic field then v is the component of the velocity perpendicular to the field. the component of velocity parallel to the field is unaffected,since the magnetic force is zero for motion parallel to the field . Hence magnetic force is related to direction of velocity only .

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