A freight train consists of 4 engines at the front, followed by 30 rail cars. Both the engines and rail cars have the same mass of 795,469 kilograms each. Each engine exerts the same force backward on the track to push the train forward. The total force of friction on the entire train is 850,978 Newtons and is evenly distributed among all of the cars and engines. Even with this friction present, the train engines are able to accelerate the train at 0.053 m/s2. What is the magnitude of the force in Newtons in the coupling between the engine and the first rail car?

explanation:

v=uf/(u-f)

= 5.-10/(5+10) convex lens has negative focal length

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electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia

one "light year" is the distance that light travels, through vacuum, in one julian year.   that's 365.25 days, of 24 hours each.