What is the Impulse Delivered by an Elevator to a Moving Package?

[teenidle]

Homework Statement

Moving at a constant speed, an elevator lifts a 1200N package 10m in 3 sec. During this time, the impulse delivered to the package by the elevator floor is
a) zero
b) 12000 Nm up
c) 3600 Ns up
d) 12000 Ns up

Homework Equations

change in momentum = net Force*time interval

The Attempt at a Solution

zero b/c if it's moving at constant speed, the acceleration is zero. therefore, net force = zero.

 

[Shooting Star]

There are two forces acting on the body -- reaction force of the elevator floor acting upward, and the weight of the body acting downward. The net force and the net impulse is zero, but the question specifically asks for the impulse delivered to the package by the floor, and thus should be 3600 Ns up. (Note that impulse is a vector quantity.)

 

[teenidle]

Thanks ShootingStar. You've been a great help.