Apulley system is because it decreases the

a. amount of effort needed to lift an object
b. amount of rope needed to lift an object
c. weight of the object
d. height that the object needs to be lifted

plz 20 points

An unknown substance is a white solid at room temperature and has a melting point of 78 °c. which of the following substances is most likely to be the identity of the unknown sample? a. naphthalene, a molecular solid with the formula c10h8 b. silica, a network solid held together by covalent bonds with the formula sio2 c. calcium chloride, an ionic compound with the formula cacl2 d. water, an molecular compound with the formula h2o