Awooden block is cut into two pieces; one is 3 times heavier than the other. a depression is made in both pieces; a firecracker is inserted in the depression and the block is reassembled. the reassembled block is placed on a rough surface and the fuse on the firecracker is lit. when the firecracker explodes, the two pieces of the block slide apart. what is the ratio of the distances traveled by each block?

Let A represent the more massive piece, and B the less massive piece.  Thus

Ma = 3 Mb

In the explosion, momentum is conserved.  We have

Va = V2 = 0

Pin = Pfinal

0 = MaVa + Mb Vb

= 3MbVa + Mb Vb

Va = - 1/3 x Vb

For each block, the kinetic energy gained during the explosion is lost to negative work done by friction on the block.

Wfr = KEf - KEi = -1/2 mbv^2

But work is also calculated in terms of the force doing the work and the distance traveled.

Mfr = Ffr delta x cos 180 degrees

= -Uk Fn x delta x = -Ukmg x delta x

Equate the two work expressions, solve for the distance traveled, and find the ratio of distances.

_-1/2mv^2 = -Uk mg x delta x

Delta x = v^2 / gUx

Delta Xa / delta Xb = (- 1/3 x Vb)^2 / Vb ^2 = 1/9

And so

(Delta x)heavy / (delta x ) light = 1/9

where are the vectors ?

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