<span>D. Atoms of all elements contain protons, but the number of protons is different for every element.
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Answer:
Time period, 
Explanation:
Given that,
The quartz crystal used in an electric watch vibrates with a frequency of 32,768 Hz, f = 32768 Hz
We need to find the period of the crystal's motion. The relationship between the frequency and the time period is given by :

T is the time period of the crystal's motion.
Time period is given by :

So, the time period of the crystal's motion is
. Hence, this is the required solution.
Answer:
The velocity of the tennis ball is 4.52 m/s.
Explanation:
Given that,
The distance covered by ball, d = 9.5 meters (due south)
Time, t = 2.1 sec
Let v is the velocity of the tennis ball. We know that the velocity of an object is given by the total distance covered divided by total time taken. It is given by :

So, the velocity of the tennis ball is 4.52 m/s. Hence, this is the required solution.