In physics, sound is a vibration that typically propagates as an audible wave of pressure, through a transmission meduim such as gas, liquid, or solid and can be heard when they reach a person's ear. How does sound help people in there lives?

When the force acting on an object points at least partially in the direction of the motion the work done is considered to be negative

You throw a small rock straight up from the edge of a highway bridge that crosses a river. the rock passes you on its way down, 7.00 s after it was thrown. what is the speed of the rock just before it reaches the water 28.0 m below the point where the rock left your hand? ignore air resistance.

Suppose that f : rn → rm and that a ∈ k, where k is a connected subset of rn . suppose further that for each x ∈ k there exists a δx > 0 such that f(x) = f(y) for all y ∈ bδx (x). prove that f is constant on k; that is, f(x) = f(a) for all x ∈ k