Newton's 2nd law:
Force = (mass) x (acceleration)
(15N) = (7 kg) x (acceleration)
Divide each side
by 7kg :
(15 N) / (7 kg) = acceleration
acceleration = (15/7) m/s²
= 2.143... m/s² (rounded)
As long as the force continues pushing it the object,
it'll continue moving about 2.143... m/s faster every
second. No limit.
Well, yes, I'll admit that the numbers WILL start changing
when it reaches a significant fraction of light-speed. If the
object never runs into anything, then it'll reach, say, 30% of
light speed after about 13 years at that rate of acceleration.
