Sample Problem
A food shipper pushes a wood crate of cabbage heads (total mass m = 14 kg) across a concrete floor with a constant horizontal force F of magnitude 40 N.
(a) How much work is done by force F, and what system does it do the work?
SOLUTION: One Key Idea is that holds here: The work W done by F can be calculated as .
The Key Idea in determining the system on which the work is done is to see which energies change. Because the crate’s speed changes, there is certainly a change.
(b) What is the increase in the thermal energy of the crate and floor?
SOLUTION: The Key Idea here is that we can relate to the work W done by Ii with the energy statement for a system.
