A particle P of mass 0.2 kg is released from rest at a point 7.2 m above the surface of the liquid in a container. P falls through the air and into the liquid. There is no air resistance and there is no instantaneous change of speed as P enters the liquid. When P is at a distance of 0.8 m below the surface of the liquid, P's speed is 6 m s^-1. The only force on P due to the liquid is a constant resistance to motion of magnitude RN.

1. Find the deceleration of P while it is falling through the liquid, and hence find the value of R.

The depth of the liquid in the container is 3.6 m. P is taken from the container and attached to one end of a light inextensible string. P is placed at the bottom of the container and then pulled vertically upwards with constant acceleration. The resistance to motion of RN continues to act. The particle reaches the surface 4 s after leaving the bottom of the container.

2. Find the tension in the string.