a partially filled bag of cement is tossed off of bridge with an initial upward velocity of 3.0 m/s. the bag has a mass of 16 kg and falls 40.0 m to the river below. determine the velocity of the bag just before striking the water. i found that and it comes out to be 28.2 m/s ( correct me if i am wrong please) b. imagine that water were replaced with a trampoline . the trampoline has a spring constant of 2000 N/m. determine the distance the bag will sink in the trampoline before coming to a stop.? i know that i have to use kinetic energy and potential energy and elastic potential energy but i dont know what to set = to zero and what not.. can someone please help me !