text: a 0.3kg mass is attached to a spring that ias a spring constant of 400 (n/m).? the spring is stretched 10cm from teh equilbrium position and is released.  when the mass is halfway back (5cm), thje speed of the mass will be about?? we can use work energy theorem.i.e. work done by all the forces(force of gravity= -0.3*9.8(.05m) +work done by spring force =1/2 k(xf^2-xi^2)  )is equql to change in kinetic energy i.e.1/2mv^2-1/2mu^2.  where u=0 .i think u should try this.thanks