4 (a) A person on a cart is using a blower to blow wind onto an umbrella, as shown in the picture below. Is he able to move this way or not? Explain your reason based on the principles taught in this class. (3 marks) CAUTION - 3- Mechanics 2020/2021 Examination The Hong Kong Polytechnic University AP20003 (b) Consider the following three cases, describe to what direction the cart may move (or not move at all) under the wind blowing from the fan. (3 marks) t (II) (III) (c) Assume the density of air is 1.29 kg/m and the blower has a venting area of 0.02 m and can blow air out with a speed of 30 m/s. Neglect the speed of air coming into the blower. How much force can it generate when blowing the air? (4 marks)