Speed!Classical Mechanics Level 1
A car is moving at a constant speed of 40km/h along a straight road which heads towards a large vertical wall and makes a sharp 90 degree turn by the side of the wall. A fly flying at a constant speed of 100km/h, starts from the wall towards the car at an instant when the car is 20km away, flies until it reaches the glass-pane of the car and returns to the wall at the same speed. It continues to fly between the car and the wall till the car makes the 90degree turn. How many trips has it made between the car and the wall?