Static equilibruim in light spring

[jinx007]

A light spring has a mass of 0.20 kg suspended from its lower end. A second mass of 0.10 kg is suspended from the first by a thread. The arrangement is allowed to come into static equilibrium and then is burned through. At this instant, what is the upward acceleration of the 0.20 kg mass. ( take g= 10 m s^-2)

Answer according to the booklet is 5.0 m s^-2

total weight acting on the first spring is 3 N ( i think so..)

Then i don't really know how to proceed...help..!

 

[aim1732]

You can do this : look at the force on the upper mass just before the string is burnt through since the spring continues to exert the same force as long as the extension does not change (which does not at that instant as the problem says), all you have to do is take out the tension of the now cut string and you will have the force and acc.