A block–spring system vibrating on a frictionless, horizontal surface with an amplitude of 5.5 cm has an energy of 28 J. If the
block is replaced by one whose mass is twice the mass of the original block and the amplitude of the motion is again 5.5 cm, what is the energy of the system?
It can't be less than 250 N or the cart wouldn't move at all. That means there is only 1 answer. It's between not enough info or 250 N. The answer is 250 N. If it was any more, there would be acceleration.