what is the potential energy initially stored in the spring? answer: 4.00 j 45) if the mass moves forward 0.5 m, how much work is done by force f? answer: 20.5 j 46) if the mass moves forward 0.5 m, how much work is done on the spring? answer: 16.25 j 47) what is the speed of the mass when it has moved forward 0.5 m? answer: 0.412 m/s 48) how far forward has the mass moved when it is in equilibrium? answer: 0.419 m 49) what is the speed of the mass when it is in equilibrium? answer: 0.419 m/s 50) how much net work has been done on the mass by the time it is in equilibrium? answer: 4.39 j 51) how far forward has the mass moved when it momentarily comes to rest? answer: 0.838 m