The engine of a small and unmanned airplane produces a known and specific sound frequency (not given). A stationary sound detection device observes that the known emitted sound frequency is 90% of the perceived sound frequency. Relative to the detection device, in which direction and at what velocity is the plane moving

the source (plane) moves away from the observer ,     v_{s} = 38.2 m / s

Explanation:

This is an exercise in the Doppler effect, which is the change in frequency due to the relative movement of the source and the observer; in this case the observer the sound detection system that is fixed and the source (plane) is mobile, in this case the relationship that describes the process is

where negative sign is for the source moving towards the observer

It indicates that the frequency of the received sound is 90% of the emitted frequency

         f '/ f = 0.90

let's substitute

           0.9 =

            = v / 0.9

The speed of sound is v = 344 m / s, let's substitute

            = 344 / 0.9

           344 \ \frac{-}{+} v_{s} = 382.2

Let's analyze this expression, to fulfill the equation the speed of the source must be positive, therefore the source moves away from the observer

           344 += 382.2

           v_{s} = 382.2 -344

           v_{s} = 38.2 m / s

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.