A65 kg roller-blade is accelerating at 5 m/s/s across the side walk. what force would be necessary for this acceleration to occur?

Newton's second law states that the force applied to an object is equal to the product between the mass m of the object and its acceleration a:

Using and , we can find the value of the force applied to the roller-blade to obtain this acceleration:

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.