PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
Four identical crates—labeled A, B, C, and D—each rest on a flat warehouse floor. At a certain instant, workers apply horizontal pushes of different magnitudes and directions to the crates. Air resistance is negligible, and each crate experiences kinetic friction of 5N opposite its motion at that instant. The table below lists, for each crate, the magnitude and direction of the applied push and the direction in which the crate is moving at that instant.
Crate | Applied push (magnitude, direction) | Direction of motion at that instant
A | 12N, east | east
B | 7N, east | east
C | 5N, west | west
D | 9N, west | east
(a) For each crate, draw a clearly labeled horizontal-axis force diagram showing the applied push and the kinetic friction force.
(b) Determine the magnitude of the net horizontal force on each crate.
(c) Rank the crates from greatest to least according to the magnitude of the net horizontal force acting on them. If any crates tie, indicate that explicitly.
(d) Identify which crates, if any, are in translational equilibrium at the instant described. Provide a concise justification for each crate based on your force analysis.