The centripetal force is directed parallel to the string and the weight of the ball is always directed downwards. Making a force balance along the direction of vertical axis: Fc cos 26 = W where Fc is the centripetal force which is equal to mv2/r W is the weight which is equal to mg
m v2 /r cos 26= mg v2 /r cos 26 = g v2 = rg cos 26 v2 = 2.1(9.81) cos 26 v = 4.30 m/s
A closed system is one in which matter does not enter or leave the system but there is exchange of energy between the system and its environment. In a closed system, the principle of energy conservation applies. The principle of energy conservation states that energy can neither be created nor destroyed but is converted from one form to another. An example of a closed system is a reaction vessel whose lid is closed.
