Mass of a particle depends on its speed . Does the attraction of the earth on the particle also depend on the paricle's speed ?

For a particle, revolving in a circle with speed, the acceleration of the particle is (a) along the tangent

Force acting on the particle moving with constant speed is

After perfectly inelastic collision between two identical particles moving with same speed in different directions, the speed of the particles become half the initial speed. Find the angle between the two before collision.