Force is Mass multiplied by Acceleration.
250 Newtons translates to 250 [Kilograms Times (Meters Per Second Every Second)].
That is to say, 250 N = 250 [kg•(m/s2)].
Then isolate the Acceleration sought by calculating 250 [kg•(m/s2)] divided by 70 kg which gives
250/70 or 3.571428571428.... (m/s2).
This Acceleration Is Equivalent To Velocity (or Speed) Going Up By 3.57 Meters Per Second Every Second Until Water Resistance Forces The 70-Kilogram Swimmer To Arm-Stroke And Leg-Kick In Order To Maintain Forward Motion At The Maximum Velocity To Which His Acceleration Took Him.