Ignoring friction, what is the mass of an object accelerating at 1.8 meters/second2 after a force of 42 Newtons has been applied to it?

100 pounds is 100 pounds no matter the object or item being weighed

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.

D.) a wheel barrow, due to the fact that where the weight is in the middle, the fulcrum is at the wheel, and the input force is at the other end