Answer:
56 m/s
Step-by-step explanation:
The time we are considering is
t = 15 s
The vertical velocity of the projectile is given by

where
is the initial vertical velocity
is the acceleration due to gravity
Substituting t=15 s, we find the vertical velocity of the projectile at that time:

where the negative sign means the direction is now downward.
The horizontal velocity does not change since there are no forces acting along that direction, so it remains constant:

So, the magnitude of the velocity at the moment of impact is
