Scientists are experimenting with a kind of gun that may eventually be used to fire payloads directly into orbit. in one test, this gun accelerates a 7.7-kg projectile from rest to a speed of 3.0 × 10³ m/s. the net force accelerating the projectile is 5.3 × 10⁵ n. how much time is required for the proiectile to come up to speed?