2. Two vehicles are moving at velocity 30 km/h & 40 km/h respectively. The
relative velocity of a vehicle w. r.t another
vehicle will be
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Ithink it is letter b, i may be wrong but i think that is the answer

Answertraveling around a circular trackexplanation"traveling around a circular track" is the best answer as you could be traveling around a circular track at a constant speed. your velocity would therefore have the same magnitude but will always be constantly direction. since acceleration is the rate of change of velocity, the rate of change will only involve the direction of velocity and not the magnitude.wrong choices: "an object at rest" does not accelerate at all"increasing speed while traveling around a curve" means that the acceleration will not be constant due to only change in direction; it will be constant due to both magnitude and direction"an object in free fall" does not necessarily change direction 

Answer (d) the universe had cooled enough for atoms to combine, protons and neutrons were too far apart to form nuclei;