A student notices that when she pulls a crate with a rope that makes a small upward…
PHYSICS · Single correct · AP · Physics 1: Algebra-based · Force and Translational Dynamics · Force and Translational Dynamics
Problem
A student notices that when she pulls a crate with a rope that makes a small upward angle with the horizontal, the required force to keep the crate moving at constant speed is less than when she pulls horizontally. Which of the following best explains this observation?
(a) Because the rope is angled, the horizontal component of the tension exceeds the total tension, so a smaller overall force is required.
(b) The upward component of the rope’s force reduces the normal force on the crate, thereby lowering the kinetic friction.
(c) The upward component of the rope’s force increases the normal force, thereby reducing friction by decreasing the coefficient of kinetic friction.
(d) Pulling upward slightly tips the crate, decreasing the contact area with the floor and thus lowering the kinetic-friction force.