A block rests on a frictionless horizontal table and is connected by an ideal string…
PHYSICS · Single correct · AP · Physics 1: Algebra-based · Force and Translational Dynamics · Force and Translational Dynamics
Problem
A 4kg block rests on a frictionless horizontal table and is connected by an ideal string over an ideal pulley to a 1kg block that hangs vertically. A student chooses to treat the two blocks together as a single system. Which of the following best explains why the tension force does not appear in the net force equation for that combined system?
(a) Tension is an internal force within the chosen system, so the forces the string exerts on the two blocks cancel when the system is analyzed as a whole.
(b) Because the string is massless, the tension force is effectively zero and therefore does not affect the system’s net force.
(c) Tension is perpendicular to the 4kg block’s motion, so it does no work and is omitted from the net force equation.
(d) The tension force on the 4kg block is fully canceled by the table’s normal force, so it plays no role in determining the system’s acceleration.