A constant rightward force (F) is exerted for a short time interval (t) on a cart that is initially at rest on an air track. This gives the cart a certain final velocity, vf.

Suppose we begin with a cart moving with the velocity vf above, and then we apply a leftward force (-F) for the same short time interval (t). What will the cart be doing after time t?

BLUE: Moves forward with twice the initial speed.

YELLOW: Moves forward with its initial speed.

PINK: Final speed is 0.

PURPLE: Cannot be determined from the information provided.