A 1kg block slides along a smooth straight groove. A position-dependent horizontal force given by F=6x2+2x (in newtons) acts in the direction of motion, where x is in metres measured from the starting point. The block is released from rest at x=0. At what displacement will its speed first reach 10m s−1?
a) 3.0m
b) 2.5m
c) 2.8m
d) 3.5m