Answer:
The number of crates is 84580.
Explanation:
mass, m = 30 kg
height, h = 0.9 mm
Power, P = 0.5 hp = 0.5 x 746 W = 373 W
time, t = 1 minute = 60 s
Let the number of crates is n.
Power is given by the rate of doing work.

Answer:
Reflection involves a change in direction of waves when they bounce off a barrier. Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or the bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves.
Explanation:
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A thermos keeps thing hot or cold by using vacuum technology to keep air from getting inside. The double walled feature of the cup is what allows the container to be "vacuum sealed". In manufacturing the air between the two walls is removed creating the seal. The lack of air keeps the heat or cold from transfering, therefore letting it remain basically the same temperature.