Blocks on Different Surfaces · PhysicsBowl 2018 #14
Physics · mechanics
Problem
Three identical wood blocks are raced across three different flat surfaces, with the faces of the blocks on the surfaces. Each block is pulled horizontally with the same force F from one edge by a light string attached to the block. Block 1 is pulled on a frictionless surface. Block 2 is pulled on a surface with a nonzero kinetic friction coefficient, and a zero static friction coefficient. Block 3 is pulled on a surface with a nonzero static friction coefficient, and the same kinetic coefficient as for Block 2, where μₖ < μₛ. If each block starts from rest and is pulled until traveling the same fixed horizontal distance, which of the following choices correctly ranks the times (t₁, t₂, t₃) it takes for each block to traverse the distance?
(A) t₁ < t₂ < t₃ (B) t₁ = t₂ = t₃ (C) t₁ < t₂ = t₃ (D) t₃ < t₂ < t₁ (E) t₂ < t₃ < t₁