A spring-mass system is initially unstretched. A constant force F is suddenly applied to the block as shown. Find the kinetic energy of the block when it passes through the new mean position.

Question

G1 Physics · Accepted Answer

The constant force F shifts the equilibrium by xₑ=F/K. Starting from x=0 at rest, when the block reaches the new mean x=F/K, work done by F is F²/K and spring energy is (1/2)K(F/K)²=F²/(2K). The remainder is kinetic: K.E.=F²/(2K). Correct option: 2.