Final Velocity = 144 m/s
Given that,
mass of the box = 10kg
distance the box travelled = 18m
initial speed = 0 m/s
Force = 40N
Force = mass x acceleration
40N = 10 x acceleration
acceleration = 40/10
acceleration = 4m/s²
where u = initial velocity
v = final velocity
a = acceleration
s = distance
v - 0 = 2(4)(18)
v = 2(4)(18)
v = 144 m/s
So the block's final velocity = 144m/s