A trolley filled with sand moves with a velocity , u on a smooth horizontal surface . At time , t=0 , sand starts to fall vertically at a constant rate from a hole at the centre of the base of the trolley . When time t=T , all the sand has fallen out .
The graph from the book shows that the trolley's velocity is constant all the way . Shouldn't the acceleration be increasing since the mass of trolley is decreasing from F=ma .
Or maybe it is because of the nature of the surface (smooth) . I am a bit confused here although it seems simple . Thanks.