A certain spring hanging from the ceiling has a force constant k = 50 N/m and a natural length 1 = 20 cm. A 0.5-kg mass is attached to the spring, and the mass is lifted so that the spring is 10 cm long. The mass is then released from rest. 4) 5) 6) 7) 8) 20 cm 10 cm 1 0.5 kg What is the speed of the mass when it is in equilibrium? (The answer is not zero.) What is the speed of the mass when the spring is again 20-cm long? How much work has been done by gravity by the time the spring is again 20-cm long? What is the maximum stretch of the spring? What is the maximum length of the spring? If the maximum length of the spring is 40 cm, what average friction force opposes the motion of the mass?