0.2 m/s! keep in mind, speed= distance divided by time :D
Sometimes negative sometimes positive, your answer is B!
As the air molecules move through the valve they have friction as they hit the walls, and its this friction that causes it to heat up.
Answer: 
Explanation:-
Single replacement reaction is a chemical reaction in which more reactive element displaces the less reactive element from its salt solution.
As zinc is more reactive than copper, it could easily displace copper from its aqueous solution and thus leads to formation of zinc (II) sulfate and pure copper.
The chemical reaction can be represented as :

The phases are represented as (s) for solid sate, (l) for liquid state, (g) for gaseous state and (aq) for aqueous state.