As shown in the figure, a small ball with a mass of 1kg passes through a fixed straight rod. The angle between the rod and the horizontal direction is 30 degrees. The dynamic friction coefficient between the ball and the rod is μ = 36. When the ball is subjected to a vertical upward tension f = 20n, what is the acceleration of the ball sliding along the rod? （g=10m/s2）

As shown in the figure, a small ball with a mass of 1kg passes through a fixed straight rod. The angle between the rod and the horizontal direction is 30 degrees. The dynamic friction coefficient between the ball and the rod is μ = 36. When the ball is subjected to a vertical upward tension f = 20n, what is the acceleration of the ball sliding along the rod? （g=10m/s2）

The ball is subjected to four forces on the rod, as shown in the figure, the gravity mg, the tension F, the elastic force FN and the sliding friction f friction. In the direction perpendicular to the rod, the combined external force is zero. In the direction parallel to the rod, the combined external force provides the force needed for the ball to accelerate. There are (f-mg) sin θ - f friction = ma (f-mg) cos θ = FN