7 A particle of mass 0.3 kg is released from rest above a tank containing water. The particle falls vertically, taking 0.8 s to reach the water surface. There is no instantaneous change of speed when the particle enters the water. The depth of water in the tank is 1.25 m . The water exerts a force on the particle resisting its motion. The work done against this resistance force from the instant that the particle enters the water until it reaches the bottom of the tank is 1.2 J .

1. Use an energy method to find the speed of the particle when it reaches the bottom of the tank.
   When the particle reaches the bottom of the tank, it bounces back vertically upwards with initial speed \(7 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). As the particle rises through the water, it experiences a constant resistance force of 1.8 N . The particle comes to instantaneous rest \(t\) seconds after it bounces on the bottom of the tank.
2. Find the value of \(t\).
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