Impinging air jets may be used to clean particles from surfaces. The kinetic energy per unit volume (J/m3) of an air jet at a surface, Er, may be written as:
E=1/2*(rho*v2)* k*d-1.3
Where:
rho = density of air (1.3 kg/m3),
v = air velocity
k = proportionality constant (0.4 mm 1.3)
d = distance from the jet nozzle (10 mm).
For a sphere (A4 = 1x10-19 J) adhered to a flat surface (A2 = 1x10-20 J), find:
1. What size of particle (diameter) could a hurricane force wind (v = 118 km/h) remove from a
surface?
2. What size of particle can be removed at v = 340 m/s (speed of sound)?
3. What air velocity would be required to remove a 1 mm particle and a 100 nm particle?

0.55x745.7j and a calculator

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.

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