Two blocks of masses 3.0 kg and 5.0 kg are placed on a smooth, horizontal surface and are connected by a light horizontal spring of spring constant k=200 N m−1k = 200\text{ N m}^{-1}k=200 N m−1. Constant horizontal forces of 24 N and 8.0 N are applied to the blocks as shown in the diagram.
What is the change in length of the spring when the blocks are moving with a common acceleration?
4.0 cm4.0\text{ cm}4.0 cm compression
9.0 cm9.0\text{ cm}9.0 cm compression
9.0 cm9.0\text{ cm}9.0 cm extension
12 cm12\text{ cm}12 cm compression