A 0.50kg cart attached to a horizontal spring (k=200Nm−1) moves on a frictionless table. When the spring is unstretched, the cart’s speed is 2.0ms−1. At what displacement from equilibrium will its speed reduce to 1.0ms−1?
(a) 0.071m
(b) 0.050m
(c) 0.087m
(d) 0.122m