Abungee jumper with mass 70.0 kg jumps from a high bridge. after reaching his lowest point, he oscillates up and down, hitting a low point eight more times in 42.0 s. he finally comes to rest 28.0 m below the level of the bridge. calculate the spring stiffness constant and the unstretched length of the bungee cord.

Ahot-air balloon takes off from the ground traveling vertically with a constant upward acceleration of magnitude g/4. after time interval δt, a crew member releases a ballast sandbag from the basket attached to the balloon. how many seconds does it take the sandbag to reach the ground? (express your answer in terms of δt)