[填空题]
A spring with k = 53N/m hangs vertically nex6:5 n.xxo bmfezkq b /n1;+let-upnt5 t tv9 d5 4s)ivdewo a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attachd)5 sidvwve 94ed to the end of the spring, where will the end of the spring line up with the ruler marks? cm