A chair of mass 10.5 kg is sitting on the horizontal floor; the floor is not frictionless. You push on the chair with a force F = 38.0 N that is directed at an angle of 43.0 ∘ below the horizontal and the chair slides along the floor.

n=142 N

Explanation:

solution:

pic 1 is attached

There is no vertical acceleration (ay = 0), so net sum of vertical forces is 0. n acts up, weight and the vertical component of F act down, so  

∑F_y =m*a_y  

n-mg-Fsin43°=0

n=142 N

if you already have the answer to (a), then just work out how many periods there are in 1 minute, and that's the answer to (c).

c.the charges if the proton and electron and gravity