A student considers two different choices of system while studying a person standing…
PHYSICS · Subjective · AP · Physics 1: Algebra-based · Force and Translational Dynamics · Force and Translational Dynamics
Problem
A student considers two different choices of system while studying a person standing inside an accelerating lift (elevator):
(i) the person alone, and
(ii) the combined system "person + lift".
Explain why the normal reaction exerted by the lift floor on the person is treated as an external force in case (i) but not in case (ii).