How long will a plane have to fly continuously with 900 miles per hour in order to cover the same distance as that from earth to the next star, proxima centauri?

I'm not sure about the distance to the nearest star, but it's probably about        4 light-years (L-y).

1 L-y = 1.86 * 10E5 mi/sec * 3600 sec/hr * 24 hr/day * 365 day/yr

1 L-y = 5.9 *10E12 mi   and 4 L-y = 2.3 *10E13 mi    distance to star

2.3 * 10E13 mi / 900 mi/hr = 2.6 * 10E10 hr       hours to star

2.6 * 10E10 hr / (24 hr/day) = 1.1 * 10E9 day     days to star

1.1 * 10E9 day / 365 day/yr = 3 * 10E6 yr = 3 million years to star

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.