A car increases its forward velocity uniformly from 20 m/s to 80 m/s while traveling a distance of 200 m. What is its accelerationduring this time?

Answer(a)   the matererials that are in contact, the two materials and the nature of their surfaces/// (b)/// the force pushing the two surfaces together, pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other

Sounds propagates through some kind of medium. usually it's air, but it goes just as well through solid objects like walls, windows etc. a soundwave will compress the (air)molecules in front of it, and if this increased density wave hits your ears, you register it as sound. solid objects like walls are a lot denser than air, this means that they will damp a wave, but also carry it easier.

An electromagnet is a material in which the current produces electromagnetism and is passed to the core.  so to fill in the blanks, choices would be better if there were.an electromagnet is a magnet produced by electric current with a metal core