force acting on a mass of 50kg when it will will accel' it from 2m/s to 9m/s in 10s?.......I got 9-2 = 7, f=ma, (50x7) = 350n Is this right?

the one im stuck on though, is a ball of mass 5kg launched upwards with 800n force gets to height 'H'. What is 'H' and what is the time from launch until ball returns to ground. (when g = 9.8m's^2)

I know this doesn't quite belong in maths forum but you guys have ben a big help in the past, any input would be much appreciated. THANKS!