Help please number 8 an 9
1 answer:
8) The reason is that MRIs use radio-waves, which are electromagnetic waves with lower frequency, and so lower energy, than X-rays.
In fact, typical frequencies for radio waves are
, while X-rays have typical frequencies of 
. Since the energy of a wave is given by
where h is the Planck constant and f the frequency, we see that the lower the frequency, the lower the energy. Therefore, radiowaves have less energy than X-rays, so they are less ionising and less dangerous than X-rays.
9) The false statement is:
a) gamma-rays are low-frequency waves.
It's actually the opposite, in fact: gamma rays are the electromagnetic waves with higher frequencies (above
).
In fact, typical frequencies for radio waves are
where h is the Planck constant and f the frequency, we see that the lower the frequency, the lower the energy. Therefore, radiowaves have less energy than X-rays, so they are less ionising and less dangerous than X-rays.
9) The false statement is:
a) gamma-rays are low-frequency waves.
It's actually the opposite, in fact: gamma rays are the electromagnetic waves with higher frequencies (above
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I assume L=120 yards as the length of the football field.
1) The average speed is given by the total distance covered by the player divided by the time taken.
The total distance covered to go from one goal line to the other and then back to the 40-yards line is
And the time taken is t=22.4 s, so the average speed of the player is
2) The find the average velocity, we should also consider the direction (and the sign) of the velocity.
In the the first part of the motion, the player goes from one goal line to the other one, so he covers 120 y. However, in the second part of the motion he goes back by 80 y. Therefore, the net displacement of the player is
and so, the average velocity is
1) The average speed is given by the total distance covered by the player divided by the time taken.
The total distance covered to go from one goal line to the other and then back to the 40-yards line is
And the time taken is t=22.4 s, so the average speed of the player is
2) The find the average velocity, we should also consider the direction (and the sign) of the velocity.
In the the first part of the motion, the player goes from one goal line to the other one, so he covers 120 y. However, in the second part of the motion he goes back by 80 y. Therefore, the net displacement of the player is
and so, the average velocity is