Let us consider two vectors A and B.
As per the question, the two vectors are perpendicular to each other.
Hence the angle between them 
We are asked to calculate the resultant of these two vectors.
As per parallelogram law of vector addition, the resultant of two vectors are-

[cos90=0]

This is the way by which we can add two perpendicular vectors.
The best and most correct answer among the choices provided by your question is the third choice or number 3.
<span>As an object falls freely toward the earth, the momentum of the object-earth system remains the same.</span>
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heat from water goes into air in ball
air expands
ping goes the dent
C. Gamma rays have more energy than infrared rays
Time period = time/no. of waves = 6/3 = 2s