Momentum (P) = Mass (kg) * Velocity (m/s)
P = M * V
P = 50 * 5
P = 250
So momentum is 250 kgm/s
In the first case, the force acting on the spring is the weight of the mass:

This force causes a stretching of

on the spring, so we can use these data to find the spring constant:

In the second case, the first mass is replaced with a second mass, whose weight is

And since we know the spring constant, we can calculate the new elongation of the spring:
Nope.
False.
The shift in spectral lines reveals only 'radial' motion ...
motion toward us or away from us. The spectrum
carries no information related to motion across the
line of sight.
Sodium (Na) is a Alkali metal so that's the answer