Two trains, each having a speed of 30 km/h, are headed toward each other on the same straight track. a bird that can fly 60 km/h flies off the front of one train when they are 60 km apart and heads directly for the other train. on reaching the other train it flies directly back to the first train, and so forth. calculate the total distance the bird travels before the trains crash.

Explanation:

Given:

Train's speed

Bird's speed

Distance between the trains  

As the two trains are moving with same velocity they will collide at a distance of 30 km. Let t be the time when they collide

so the bird will be flying with the given velocity for 1 hr before the train collide. Let d be the distance travelled by bird

heat the gas and measure the pressure

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