Two cars collide at an intersection. one car has a mass of 900 kg and is moving 10 m/s to the north, while the other has a mass of 1000 kg and is moving 7 m/s to the south. what is their combined momentum?

2000 kgm/s to the north.  

Explanation:

For any   colliding bodies, momentum must be conserved.

In this case we are required to find the momentum before collision.

Since the two cars are moving to different direction, we are going to take one velocity as negative.

∴ (900×10) + (1000× -7) = 9000 + - 7000

                                       = 9000 - 7000

                                       = 2000 kgm/s

Since the answer is positive and we had taken the velocity due north as positive, the combined momentum is 2000 kgm/s to the north.  

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