Input heat, Qin = 4 x 10⁵ J
Output heat, Qout = 3.5 x 10⁵ J
From the first Law of thermodynamics, obtain useful work performed as
W = Qin - Qout
= 0.5 x 10⁵ J
By definition, the efficiency is
η = W/Qin
= 100*(0.5 x 10⁵/4 x 10⁵)
= 12.5%
Answer: The efficiency is 12.5%
The frequency doesn't change. If the wavespeed increases, then the wavelength must also increase ... It's just the distance the wave travels during each complete wiggle.
The average speed is 20.8 m/s
Explanation:
The average speed for the trip is given by:

where
d is the distance covered
t is the time elapsed
For the trip in this problem, we have:
d = 187 km = 187,000 m is the distance travelled
The initial time is 10:00 pm while the arriving time is 12:30 am: this means that the time elapsed is 2.5 hours. Converting into seconds,

Therefore, the average speed for the trip is

Learn more about average speed:
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