Which statement best explains that sound waves are pressure waves?
2 answers:
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Answer:
t = 12 s
Explanation:
To find the time in which the police reaches the thief you write the equation of motion of both thief and police:
The thief has a constant velocity, the position is then given by:
(1)
The police has an acceleration, then the position is:
(2)
the time in which the police reaches the thief is when their positions are equal, that is, when expression (1) equals expression (2). But before you calculate the acceleration of the police:
you replace this values in (2) and you equal the expression (1) and (2) (with vo = 0):
one root is t = 0s, but it is omitted because is the momment in which the thief pass in front of the police. The other root is:
hence, the time is 12 s
Answer:
Some work input is lost to friction
Explanation:
The efficiency of a machine is defined as:
(1)
where
is the work output
is the work input
Due to the law of conservation of energy, the work output can never be larger than the work input (because energy cannot be created). Moreover, in real machines part of the work input is lost due to the presence of frictions: as a result, part of the energy in input is converted into thermal energy or other forms of energy, and so the work output is smaller than the work input, and so the ratio (1) becomes less than 1, and so the efficiency is less than 100%.