An unstretched ideal spring hangs vertically from a fixed support. A 0.4 kg object is then attached to the lower end of the spring. The object is pulled down to a distance of 35cm below the unstretched position and released from rest at t=0s. A graph of the subsequent vertical position 'y' of the lower end of the spring as a function of 't' is shown to the right where y=0 is when the spring was initially unstretched. What is the spring's length when it is unstretched?
3 answers
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just calculate the velocity at all the time given in the options (there is a graph too)