A trolley containing sand moves on a perfectly smooth horizontal track. Sand leaks vertically downward through a hole in the trolley. Assume each sand particle has the same horizontal velocity as the trolley at the instant it leaves. Which statements are correct?
Select all that apply

Question

A trolley containing sand moves on a perfectly smooth horizontal track. Sand leaks vertically downward through a hole in the trolley. Assume each sand particle has the same horizontal velocity as the trolley at the instant it leaves. Which statements are correct?

Select all that apply

G1 Physics · Accepted Answer

Let the trolley speed be v. At the instant a small mass of sand leaves, its horizontal velocity relative to the trolley is zero, so its horizontal ground velocity is also v. Therefore the escaping sand carries away exactly the same horizontal momentum per unit mass as the trolley already has. There is no horizontal rocket thrust because there is no horizontal relative exhaust velocity. Hence the trolley's horizontal speed remains constant: A is correct. Loss of mass alone does not imply acceler…