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:
maximum work is done in the case
D) Clark pushed a crate from the chair, 16 meters across the room, doing 144 J of work.
Explanation:
As we know that the Work done is product of force and displacement
So we have
A) Steve put in 50 J of work moving a box 50 meters.
So here we have
50 = F . 50
F = 1 N
B) Doing 400 J of work, Penny pushed her cat 80 meters.
So here we have
400 = F . 80
F = 5 N
C) Samantha did 365 J of work dragging a wagon across 73 meters of lawn.
So here we have
365 = F . 73
F = 5 N
D) Clark pushed a crate from the chair, 16 meters across the room, doing 144 J of work.
So here we have
144 = F . 16
F = 9 N
So maximum work is done in the case
D) Clark pushed a crate from the chair, 16 meters across the room, doing 144 J of work.
Answer:
-0.832 m/s²
Explanation:
Since acceleration a = (v - u)/t where u = initial velocity of astronaut = +14.7 m/s (positive since he is moving towards the right), v = final velocity of astronaut = +4.8 m/s (positive since he is moving towards the right) and t = time taken for velocity change = time interval = 11.9 s.
Since a = (v - u)/t
Substituting the values of the variables into the equation, we have
a = (v - u)/t
a = (+4.8 m/s - (+14.7 m/s))/11.9 s
a = (4.8 m/s - 14.7 m/s)/11.9 s
a = -9.9 m/s ÷ 11.9 s
a = -0.832 m/s²
So, the astronaut's average acceleration is -0.832 m/s²
The heat of sublimation actually has two components, the heat of solidification (actually melting, since this is going in the reverse direction) and the heat of vaporization since you are transforming the solid to a gas. The energy required is the same, even though you do not actually go through a macroscopic melting phase. So the sublimation energy will be much greater than the heat needed for just melting, given the same mass.
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Force = (kg)(m/s^2)
If we plug in the values, force = (55kg)((20m/s)/0.5s) = (55g)(40m/s^2) = 2200N