A mass 10kg moving with a speed 10 cm/s on a smooth horizontal surface hits a spring as shown in figure.  Work done by the spring force on the mass is ,

from work energy theorem work done = change in KE W = KEfinal-KEinitial; mass comes to rest finally , KEfinal=0 Work done by spring  =   - K.E. of mass work done=    −12(10)  (0.1)2  work done by spring  =    −  0.05 joule