posted by jessy .
a plank of mass 5kg is placed on a frictionless horizontal table. further a block of mass 2kg is placed over the plank. A mass-less spring of natural length 2m is fixed to the plank by its one end. The other end of spring is compressed by the block by half of its springs natural length. The system is now released from the rest. What is the velocity of the plank when block leaves the plank?