A glob of sticky putty is thrown against a slightly open door so that it sticks on impact and gives the door a momentum of 1.4 kg m/s. A rubber ball with exactly the same mass and velocity as the sticky putty strikes the door and bounces back at its initial speed in the opposite direction. What impulse does it impart to the door?

2.8 kgm/s

1.4 kgm/s

0.70 kgm/s

0 kgm/s