Newton’s second law as F = dp/dt

A cart rolls to the right on a frictionless horizontal track at speed $v$. Dry sand leaks from a hole in the floor of the cart and falls straight down relative to the cart, so each grain keeps the cart’s horizontal velocity at the instant it leaves. No one pushes the cart. Gravity and the normal force are vertical.

Before any derivation:

As the remaining mass of the cart-plus-sand decreases, what happens to the speed of the remaining cart?

Which reason is closest to your prediction?

Confidence