just analyze it in this way:
20cos30*=10( radical 3 )
20sin30*=10
Answer: The system internal energy is 40 Joules.
Explanation: As suggested, the formula 
should be used. 70 Joules worth of thermal energy are added, and the system does 30 Joules worth of work (energy expenditure).
Answer:
find possible answers to problems
Explanation:
Science can be defined as a branch of intellectual and practical study which systematically observe a body of fact in relation to the structure and behavior of non-living and living organisms (animals, plants and humans) in the natural world through experiments.
Science is applied to many fields in the world such as medicine, information technology, cybersecurity, engineering, environmental etc.
Basically, knowing how to apply science simply means a scientist understands the appropriate method or technique to be used in the application of a technology such as when solving a problem.
Creativity implies being able to use an idea to proffer solutions to a problem in an intelligent manner.
Hence, a scientist should be creative in order to find possible answers to problems.
The answer is solely based on the length of space between atoms. In gaseous mediums, atoms are generally quite far apart allowing waves to be undisrupted in the process. In solids and liquids, sound waves are trapped/diluted in the relatively close atom distances
There are really only two choices there ... hot air rising is one PART of a convection current, and convection current happens because of physical properties.
Fuel can burn in a furnace because of its chemical properties. <em>(B)</em>
