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[sassy]

A dog jumps from a building at a height of 23 m above a net w/a 3 kg puppy in her mouth. The dog has a mass of 35 kg. When the dog and the puppy land in the net, it bends 3 cm before tossing her and the puppy in the air again.
1. If the net is considered to be at a height of 0 m, what is the potential energy at the top of the building?
2. What is the total kinetic energy just before they hit the net?
3. What is the magnitude of the total momentum just before they reach the net?
4. What is the spring constant of the net?
5. What is the total external force on the system?
6. What is the magnitude of the impulse of the gravity acting on the system between the time they jump from the building and just before they hit the net?
7. What is the acceleration of the system as they fall?
I figured out most of the question. But I am still stuck on the spring constant. I have tried three equations but am not getting the right answer. Any help??