1. Which of the following statements about mechanical waves is true?
1 answer:
1) <span>a. mechanical waves require a medium to travel through
In fact, mechanical waves cannot travel trough empty space, but they always require a medium for their propagation. (on the contrary, electromagnetic waves can also travel through empty space)
2) d</span><span>. gamma rays
In fact, gamma rays are the radiations with shortest wavelength on the electromagnetic spectrum (range in the picometer). Correspondingly, this is the radiation with highest energy, because the energy of the radiation is inversely proportional to its wavelength, according to:
</span>
where h is the planck constant, c the speed of light and
the wavelength.
3) <span>d. Infrared have lower frequency than x-rays
In fact, infrared radiation has frequency in the range of the THz (terahertz, </span>
), while x-rays have frequency in the range of hundreds of PHz (Petahertz, 
).
4) <span>d. parallel
In longitudinal waves, the oscillations of the wave (such as the motion of the particles in a compression wave) occur in the direction parallel to the direction of propagation of the wave itself.
5) </span><span>c. gases
Sound travels slowest in gases. In fact, the speed of sound is proportional to the density of the medium: the more dense the medium is, the faster is the sound in that medium, and vice-versa. Since gases are less dense than liquids and solids, sound travels slowest in gases. The reason is that sounds propagates through the oscillations of the molecules of the medium; if the medium is less dense (such as in gases), it takes more time to transmit the sound through the medium itself.</span>
In fact, mechanical waves cannot travel trough empty space, but they always require a medium for their propagation. (on the contrary, electromagnetic waves can also travel through empty space)
2) d</span><span>. gamma rays
In fact, gamma rays are the radiations with shortest wavelength on the electromagnetic spectrum (range in the picometer). Correspondingly, this is the radiation with highest energy, because the energy of the radiation is inversely proportional to its wavelength, according to:
</span>
where h is the planck constant, c the speed of light and
3) <span>d. Infrared have lower frequency than x-rays
In fact, infrared radiation has frequency in the range of the THz (terahertz, </span>
4) <span>d. parallel
In longitudinal waves, the oscillations of the wave (such as the motion of the particles in a compression wave) occur in the direction parallel to the direction of propagation of the wave itself.
5) </span><span>c. gases
Sound travels slowest in gases. In fact, the speed of sound is proportional to the density of the medium: the more dense the medium is, the faster is the sound in that medium, and vice-versa. Since gases are less dense than liquids and solids, sound travels slowest in gases. The reason is that sounds propagates through the oscillations of the molecules of the medium; if the medium is less dense (such as in gases), it takes more time to transmit the sound through the medium itself.</span>
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Answer:
a) , b)
Explanation:
The magnitude of torque is a form of moment, that is, a product of force and lever arm (distance), and force is the product of mass and acceleration for rotating systems with constant mass. That is:
Where is the angular acceleration, which is constant as torque is constant. Angular deceleration experimented by the unpowered flywheel is:
Now, angular velocities of the unpowered flywheel at 50 seconds and 100 seconds are, respectively:
a) t = 50 s.
b) t = 100 s.
Given that friction is of reactive nature. Frictional torque works on the unpowered flywheel until angular velocity is reduced to zero, whose instant is:
Since , then the angular velocity is equal to zero. Therefore: