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T T EnergyiKinetie.. e 6)A 20 | u.mm..mun-nenmwhnu.m\"a.--l-'h"""' 20 kg a. What potential energy does the rock-Earth system possess relative to the base of the cliff? kJ R b. The rock falls without rolling from the cliff. What is its kinetic energy just before it strikes the ground? kJ e e e e Red . What is the rock's speed as it hits the ground? m/s 7) Kelli weighs 420 N, and she sits on a playground swing that hangs 0.40 m above the ground. Her mom pulls the swing back and releases it when the seat is 1.00 m above the ground. a. How fast is Kelli moving when the swing passes through its lowest position? m/s b. If Kelli moves through the lowest point at 2.0 m/s, how much work was done on the swing by friction? J