A charged particle is placed in a uniform magnetic field and negligible gravitational field. When released it will exhibit constant

Constant velocity

Explanation:

The Lorentz force acting on the particle is given by F = Bqvsinθ where B =    magnetic field strength, q = charge, v = speed of charge and θ = angle between v and B.

If the charge is released with a velocity, v, it experiences a force, F = Bqvsinθ. Since F = ma, Bqvsinθ = ma and a = Bqvsinθ/m. So, since all the variables are constant, the charged particle exhibits no acceleration since the velocity is constant.

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.