Sample Problem

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.

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