In a bizarre but harmless accident, a watermelon fell from the top of the Eiffel Tower. How fast was the watermelon traveling when it hit the ground 6.40 seconds after falling?

v = 62.7 m/s

Explanation:

Assuming no air resistance, the only force acting on the watermelon while it was falling, was the one due to the gravity.This means that the object fell down with a constant acceleration which magnitude is equal to 9.8 m/s2.Applying the definition of acceleration, and assuming that the watermelon was dropped, so initial velocity is just zero, we can find the speed when it hit the ground as follows:

       

The watermelon was traveling at a speed of 62.7 m/s when it hit the ground.

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