A15 kg box is accelerated from 15m/s to 30 m/s in 36 seconds. what is the net force exerted on the box?

Acceleration = (change in speed) / (time for the change)

Acceleration = (30 m/s - 15 m/s) / (36 sec)  = 

                                   (15 m/s) = (36 sec)  =  5/12  m/s²

Force = (mass) x (acceleration)

Force =  (15 kg) x (5/12 m/s²)  =  6.25 newtons  (about 1.4 pounds)