The hollow tube is pivoted about a horizontal axis through point o and is made to rotate in the vertical plane with a constant counterclockwise angular velocity ω= 3 rad/sec. if a 0.2 lb particle is sliding in the tube toward o with a velocity of 6 ft/sec relative to the tube when the position θ= 300 is passed, calculate the magnitude n of the normal force exerted by the wall of the tube on the particle at this instant.