John is a nuclear scientist who works at the Fermi lab. Today, in front of him he has four samples, sample A, sample B, sample C, and sample D. Sample A is the naturally occurring uranium. Sample B is enriched uranium. Sample C is the U-238, and sample D is the U-235. He needs to figure out how to best use them. Which smaple would not be fissionable, sample C or sample D? Hint: Naturally occurring uranium is composed almost entirely of two isotopes, uranium-238 (99%) and uranium-235 (1%). It is the uranium-235 that is fissionable (will undergo fission) and therefore, this is the uranium isotope than can be used for fuel in a nuclear reactor. For uranium to be used as fuel, the percent of uranium-235 must be increased to at least 3%. Uranium in which the U-235 content is more than 1% is called enriched uranium. Somehow, the two isotopes must be separated so that enriched uranium is available for use as fuel. Separating the isotope by chemical means (chemical reactions) is not successful because the isotopes have exactly the same chemistry. The only essential difference between U-238 and U-235 is their atomic masses; as a result, the two isotopes are separated by a physical means that takes advantage of the difference in mass.
Ans: sample C

Two friends met after 20 years and had a beer together. Vlad was a geologist and studied earthquakes. Mort was a pedologist and studied soils. They had some interesting conversations that night. Which friend studied more about seismic waves? Hint: Geologists study earthquake waves to "see" Earth's interior. Waves of energy radiate out from an earthquake's focus. These waves are called seismic waves ( Figure below ). Seismic waves go different speeds through different materials. They change speed when they go from one type of material to another. This causes them to bend. Some seismic waves do not travel through liquids or gases. They just stop. Scientists use information from seismic waves to understand what makes up the Earth's interior.
Ans: Vlad

Keith was reading a book on climate. He found an interesting table that showed the climatic conditions of the earth in two different times, time A and time B. Time A showed earth's climatic condition in the previous century. And, time B showed earth's climatic condition in the present century. Keith was amazed to see how the world has changed in just a century. Which period would be more harmful for habitat of species, time A or time B? Hint: Another major cause of extinction is global warming , which is also known as global climate change. During the past century, the Earth's average temperature has risen by almost 1C (about 1.3F). You may not think that is significant, but to organisms that live in the wild and are constantly adapting to their environments, any climate change can be hazardous. Recall that burning fossil fuels releases gasses into the atmosphere that warm the Earth. Our increased use of fossil fuels, such as coal and oil, is changing the Earth's climate. Any long-term change in the climate can destroy the habitat of a species. Even a brief change in climate may be too stressful for an organism to survive. For example, if the seas increase in temperature, even briefly, it may be too warm for certain types of fish to reproduce.
Ans: time B

Bob works as a scientist for a large fishing company in Norway. Norway's government has strict regulations on fishing to protect its fish stock. Part of Bob's job is to provide the government with fish mortality data. Today, he has two samples of fish to investigate, sample A and sample B. Bob concluded sample A had natural mortality, but sample B had fishing mortality. For which sample disease would not be a cause of death, sample A or sample B? Hint: Fish mortality is a parameter used in fisheries population dynamics to account for the loss of fish in a fish stock through death. The mortality can be divided into two types: Natural mortality: the removal of fish from the stock due to causes not associated with fishing. Such causes can include disease, competition, cannibalism, old age, predation, pollution or any other natural factor that causes the death of fish. In fisheries models natural mortality is denoted by (M).[1] Fishing mortality: the removal of fish from the stock due to fishing activities using any fishing gear.[1] It is denoted by (F) in fisheries models.
Ans: sample B