Radio waves have many uses—the category is divided into many subcategories, including microwaves and electromagnetic waves used for AM and FM radio, cellular telephones and TV.
The lowest commonly encountered radio frequencies are produced by high-voltage AC power transmission lines at frequencies of 50 or 60 Hz. These extremely long wavelength electromagnetic waves (about 6000 km) are one means of energy loss in long-distance power transmission.
Extremely low frequency (ELF) radio waves of about 1 kHz are used to communicate with submerged submarines. The ability of radio waves to penetrate salt water is related to their wavelength (much like ultrasound penetrating tissue)—the longer the wavelength, the farther they penetrate. Since salt water is a good conductor, radio waves are strongly absorbed by it; very long wavelengths are needed to reach a submarine under the surface.
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Answer:
313.6 m
Explanation:
From the question given above, the following data were obtained:
Time (t) = 8 s
Acceleration due to gravity (g) = 9.8 m/s²
Height (h) =?
The height at which the package was dropped can be obtained as follow:
h = ½gt²
h = ½ × 9.8 × 8²
h = 4.9 × 64
h = 313.6 m
Thus, the package was at a height of 313.6 m when it was dropped.
(a)
The work done on the projectile is 9375 joule.
The work on the projectile is calculated as
W=F×d
=1250×7.5
=9375 joule
(b)
The speed of the projectile after 7.5 m is 27.38 m/s
First we need to find out the acceleration of the projectile
F=m×a
1250=25×a
a=50 m/
Now the velocity of the projectile after 7.5 m is calculated as
v^2=u^2+2a×s
v^2=0+2×50*7.5
v=27.38 m/s
