Answer:
f1 = 12.90 Hz
Explanation:
To calculate the first harmonic frequency you use the following formula for n = 1:

( 1 )
It is necessary that the unist are in meters, then you have:
L: length of the string = 60cm = 0.6m
M: mass of the string = 0.05kg
T: tension on the string = 20 N
you replace the values of L, M and T in the expression (1) for getting f1:

Hence, the first harmonic has a frequency of 12.90 Hz
Answer:
It is a instrument used to measure the distance traveled by a vehicle.
Explanation:
This is what it looks like ↓
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Potential Difference given is : 2V
Resistance is : 2 ohms
By Ohm's Law, one can easily utilize the relation :

Where, { v , i , r } are the potential difference, current and Resistance Respectively.
Hence,

Hence, the Current is 1 Ampere
The 4 significant figures of 31,546,000 are all 8 of the digits.