1) A 1.0-kg laboratory cart moving with a velocity of 0.50 m/s due east collides with and sticks
to a similar cart initially at rest. After the collision, the two carts move off together with a
velocity of 0.25 m/s due east. The total momentum of this frictionless system is
1) zero after the collision
2) the same before and after the collision
3) greater before the collision than after the collision
4) zero before the collision