a 60kg sprinter accelerates from rest at 2.5m/s east for 4s. what force is acting and what is his final speed?
Your "2.5 m/s" must be the acceleration, and should have been written 2.5 m/s^2.
The force acting is
F = m a = 60*2.5 = 150 N
The final speed is Vfinal = a*t
where t = 4.0 s. That would be 10 m/s