2. A railway car on a horizontal frictionless track initially has mass m and speed vo. Sand is then dropped vertically downward onto the car, starting from rest at a vertical height h. The sand hits the card at a constant rate u (mass/time). Assume that when the sand hits the cart, the sand instantaneously comes to rest relative to the cart. If the sand starts hitting the cart at t = 0, find the velocity of the cart as a function of time.

2. A railway car on a horizontal frictionless track initially has mass m and speed vo. Sand is then dropped vertically downward onto the car, starting from rest at a vertical height h. The sand hits the card at a constant rate u (mass/time). Assume that when the sand hits the cart, the sand instantaneously comes to rest relative to the cart. If the sand starts hitting the cart at t = 0, find the velocity of the cart as a function of time.