A tennis ball with a mass of 0.1kg falls off the roof of a building 10.4 meters tall. How long does it take for the ball to hit the ground ?

1.46 seconds

Explanation:

The key formula ==>            H = 1/2 G T²

                                        10.4 = 1/2 (9.8) T²

Divide each side by  4.9 :  T² = 10.4 / 4.9

                                          T = √ (10.4/4.9) = 1.46 seconds .

The mass of the ball doesn't make any difference.  If not for air resistance,

a feather and a school bus, dropped from the same height at the same time,

would fall together, and hit the ground at the same time.  We've known this

for roughly 600 years now, and I suspect you learned it in the same high

school class where your question came from.

the total distance traveled by the car is

30km + 49km = 79 km .