The correct option is C) The angle between the vectors is 120°.
Why?
We can solve the problem and find the correct option using the Law of Cosine.
Let A and B, the given two sides and R the resultant (sum),
Then,

So, using the law of cosines, we have:

Hence, we have that the angle between the vectors is 120°. The correct option is C) The angle between the vectors is 120°
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Answer:
D. 550 Hz
Explanation:
Frequency for string is given by

where v is the speed of the wave, L = m is the length
Frequency is inversely proportional to the Length of the string

from above relation we can write

The newly shortened string has 4/5 the length of the full string .i,e

Hence option D is correct
Answer:
The magnetic field is doubled.
Explanation:
What happens to the strength of the magnetic field if one more 1.5 v dry cell is added?
The magnetic field due to a current carrying conductor is directly proportional to the current flowing in the wire.
If we connect one more battery of 1.5 V so the voltage is doubled and according to the Ohm's law, as the resistance of wire is constant, so the current in the wire is also doubled.
When the current doubles, the magnetic field produced by the wire is also doubled.