Chapter 6

Mechanical Energy

Kinetic Energy is the energy of motion of any moving object.

The Work-Energy Theorem:


Example 6

A 4.1 kg box of books is lifted vertically from rest a distance of 1.6 m by an upward applied force of 60.0 N. Find (a) the work done by the applied force, (b) the work done by gravity, and (c) the final speed of the box.



Example 7

The figure shows two industrial spies sliding an initially stationary 225 kg floor safe a displacement of magnitude 8.50 m, straight toward their truck. The push of Spy 001 is 12.0 N, directed at an angle of downward from the horizontal: the pull of Spy 002 is 10.0 N, directed at above the horizontal. The magnitudes and directions of these forces do not change as the safe moves, and the floor and safe make frictionless contact. (a) What is the net work done on the safe by forces and during the displacement ? (b) During the displacement, what is the work done on the safe by the gravitational force and what is the work done on the safe by the normal force from the floor? (c) The safe is initially stationary. What is its speed at the end of the 8.50 m displacement?


Mechanical Energy Part 2