Most of the question 1 is chopped off so I'll try my best to answer.
1ai) In a telephone, the sound is converted into electrical signals before being sent through the wire before converted back into sound.
1aii) Sound travels by the collision between particles. In solids, the particles are closely packed (as compared to air molecules) and thus collide with their neighbors quickly after being disturbed, allowing for sound to be passed on at a faster rate.
b) Can't help much on this one.
They would just have to box in a higher weight class
Answer:
Because the molecules are not packed together as much than the air, in a fixed volume of helium there are fewer particles than in the same fixed volume of air.
This means that the mass of the fixed volume of helium is smaller than the one of air, and then the density, defined as mass/volume, is also smaller.
This is why the balloon floats, because the air is denser, it tries to go down, pushing the ballon upside.
The case is similar for a piece of metal in water, as the metal is way denser than the water, the metal will sink, but for something not as dense, like a balloon with air, the balloon will remain in the surface of the water.
The particle has an acceleration vector with one component directed toward the center of its orbit, and the other directing tangentially to its orbit. Call these components 
(
for center) and 
(
for tangent). Then its acceleration vector has magnitude
We have
where 
is the particle's speed and 
is the radius of orbit, so
We're given that the particle's speed changes at a rate of 23.1 m/s^2. Its velocity vector points in the same direction as , i.e. perpendicular to , so
Then the magnitude of the particle's acceleration is
Grav Force = GMm/r squared. M is earth's mass. m is the probe. r is distance to centre of earth.Given that 600 = GMm/(10,000^2).GMm = 600x(10,000^2) for 10, 000 milesGMm = ? x (20,000^2) for 20, 000 milestherefore600x(10,000^2)=? x (20,000^2)therefore [600x(10,000^2)]/(20,000^2)=? [600x(1x1)]/(2x2)=? [600/4]=? ?=150lb.Same procedure for b and c.Please ask if you want further help.
