6. In this question, i and j are unit vectors which are horizontal and vertically upwards. The units for postion are metres, A particle has mass 4 kg. (a) Write down the weight of the particle in vector form. [1] The particle is acted on by two forces (3i + 2j) N and (-21 + 8j) N. (b) Find the acceleration of the particle. [3] The particle is initially at rest at a point with position vector (4i + 7j) m. (c) Find the position of the particle after 3s. [4] (d) Find the time at which the particle is at the same height as the origin