A generation is about one third of a lifetime. Approximately how many generations have passed since the beginning of recorded history? Half the life expectancy of a human is of the order of 10^9 s

It's have to be 12 or idk

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 

The sun's gravitational pull is weaker on the planets that are closer to it, i think.