The porosity (fraction of void space) in a soil can be measured as follows: first, the total volume of a moist sample is calculated. for a cylindrical sample (obtained from a core, for example) the total volume is given by the expression where r is the radius of the cylinder and h is its height. the sample is then dried thoroughly in an oven and weighed. the mass mdry is the mass of the solids only. the volume of the solids vs is then computed by dividing the dry mass by the average density of the solid materials. assume that the solids have an average density of 2.6 g/cm3 the porosity n is then computed from the expression: vt -vs vt n- calculate the porosity of a soil sample given the following parameters, and express your answer with the correct number of significant figures. haylinder (cm) mdry (g) oylinder (cm) 2.508 10.0 425.0

Scientist: cross-sections of stalactites—calcite formations deposited on cave ceilings by seeping water—can reveal annual variations in rainfall in particular areas over hundreds and thousands of years. we often found that when—according to these cross-sections—drought occurred in a particular area, it coincided with the collapse of an ancient society in that area. i hypothesize that drought reduced agricultural productivity in these areas, thereby leaving these societies without the resources needed to handle internal stresses and external threats. which of the following, if true, would most weaken the support for the scientist's hypothesis? a. many droughts indicated in the cross-sections of stalactites do not correspond with the collapse of a society in that area. b. information from the cross-sections of stalactites alone cannot reveal the level of agricultural output in an area at a particular time. c. most of the societies that collapsed during droughts did so when internal power struggles coincided with military raids from neighboring societies. d. most of the societies that collapsed during droughts maintained large stockpiles of food and water at the time of their collapse. e. information from stalactites also suggests that the collapse of some societies coincided with periods of abnormally high rainfall.