The magnitude of the force required to compress an imperfect horizontal spring a distance x is given by f=kx+bx3 where k = 120 n/m and b = 18 n/m3. if you use a 3.5-kg block to compress the spring a distance of 2.2 m and then let it go, what speed will the block have when it leaves the spring? assume the surfaces are smooth enough that any frictional forces can be neglected.