4. A stone is projected over horizontal ground from a point O on the ground. The velocity of projection is 30 ms" at 40 to the horizontal. The effects of air resistance should be neglected. (a) State the modelling assumptions used in the standard projectile model. [2] (b) The stone is at a horizontal distance x m from the point of projection and y m above the ground f seconds after projection. Write down an expressions for x and y in terms of t. [2] The stone passes directly over a wall which is at a horizontal distance of 34 m from O. (c) Find the time taken to reach the wall. [2]

(d) Determine the speed of the stone as it passes over the wall. Calculate also the angle between the direction of motion of the ball and the horizontal at that time, making it clear whether the ball is rising or falling. [8]