Pure substances can be elements made up exclusively of one kind of atom, or they can be compounds made up of molecules that include two or more elements. Mixtures can be homogeneous or heterogeneous depending on how finely mixed the components are.
Answer:
The speed of the block is 4.96 m/s.
Explanation:
Given that.
Mass of block = 1.00 kg
Spring constant = 500 N/m
Position 
Coefficient of friction = 0.350
(A). We need to calculate the speed the block has as it passes through equilibrium if the horizontal surface is friction less
Using formula of kinetic energy and potential energy

Put the value into the formula




Hence, The speed of the block is 4.96 m/s.
Potential energy because it has enough energy to do work but non has been done yet.
An ecosystem is the diversity of many communities of organisms where they interact with living as well as non living thing whereas community contains the variety of populations of different species. Hope this helps x