Answer
a. No.
b. Yes.
Work Step by Step
a. When you walk down the hallway, your hand’s force and gravity are both perpendicular to the horizontal displacement, and neither force does any work. The net work is zero because the change in kinetic energy is zero.
b. When you ride an escalator up, your hand does positive work on the briefcase while gravity does negative work on the briefcase, of equal magnitude. The net work is zero. The net work is zero because the change in kinetic energy is zero.
