The friends take a few minutes to discuss their ideas. which of amy's comments with respect to a charged particle moving in a magnetic field is false? "the magnitude fb of the magnetic force exerted on the particle is proportional to the magnitude of the charge q and to the speed v of the particle." "the magnetic force acting on a charged particle moving in a magnetic field is perpendicular to the particle's velocity." "if the magnetic force is always perpendicular to the velocity, the path of the particle is a straight line." "the work done by the magnetic force on the particle is zero."

The statement "if the magnetic force is always perpendicular to the velocity, the path of the particle is a straight line" is false.

Explanation:

The equation for the magnetic force on a charge q moving at velocity v on a magnetic field B is given by the (vectorial) Lorentz Force Law

From it we can clearly see that the magnitude of the magnetic force exerted on the particle is proportional to the magnitude of the charge q and to the speed v of the particle, and that it is also perpendicular to the particle's velocity. This means that at each instant it moves perpendicularly to the force, so the work done by the magnetic force on the particle is zero.

The statement "if the magnetic force is always perpendicular to the velocity, the path of the particle is a straight line" is false not only for this but for any force, a force always perpendicular to a velocity will curve the trajectory.

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.