1. LAW OF SUPERPOSITION: When observing rock layers, the oldest rocks/fossils can be found at the , while the youngest can be found at the . a. middle, bottom
b. left, right
c. bottom, top
d. top, bottom

2. Two rock layers contain fossils of similar organisms. What is likely true of these rock layers?
a. They were from different environments.
b. They had advantageous traits.
c. They had analogous structures.
d. They were from the same time period.
ps this is science

The boy of mass 30 kg is at r1= 2 meters from the fulcrum. of the girl is 45 kg, at what r2 must she sit so that they are balanced ?

Uranium has two naturally occurring isotopes. 238u has a natural abundance of 99.3% and 235u has an abundance of 0.7%. it is the rarer 235u that is needed for nuclear reactors. the isotopes are separated by forming uranium hexafluoride uf6, which is a gas, then allowing it to diffuse through a series of porous membranes. 235uf6 has a slightly larger rms speed than 238uf6 and diffuses slightly faster. many repetitions of this procedure gradually separate the two isotopes. what is the ratio of the rms speed of 235uf6 to that of 238uf6? express your answer to five significant figures.

The first law of thermodynamics states that heat added to a system is neither created nor destroyed but is as it changes into other forms of energy.