A rocket of mass 100,000 kg undergoes an acceleration of 2m/s2. Show that the force being developed by the rocket engines is 2000,000 N.

I assume you meant to write "200,000 N," not "2000,000 N," correct?

Simply use F=ma. You have values for m (mass) and a (acceleration). But whoever wrote this question should have noted that the rocket is accelerating in a horizontal direction, since for the rocket to rise vertically would take more force than that to overcome gravity -- note that the rockets weight is 100,000 Kg x 9.8 m/s^2 = 980,000 N.