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• Explain how relative directions of force and displacement determine whether the work done is positive, negative, or zero. 7.2.Kinetic Energy and the Work-Energy Theorem • Explain work as a transfer of energy and net work as the work done by the net force. • Explain and apply the work-energy theorem. 7.3.Gravitational Potential Energy
To calculate the work done on an object by a force during a displacement, we use only the force component along the object's displacement. The force component perpendicular to the displacement does zero work •Caution: for all the equations we have derived so far, the force must be constant, and the object must be rigid.
Example: A book is lifted a height h by an external force (my hand) at constant velocity. Here, F net = 0 (since constant velocity), so W net = 0. The book does not speed up or slow down, so KE = 0. Hence, W net = KE The Work-KE Theorem provides a short-cut in some problems: x F ext v i v f F fric m
When force and displacement are perpendicular to one another or when either the force or displacement is zero, zero work is defined. If a block is moving on a smooth horizontal surface, no work is done. We can explore a zero work example, the only requirement is that the force exerted be perpendicular to the displacement.
In this collection, the reader will find some exemplary solutions of Introductory Physics problems that show the efficient methods and approaches. It is recommended to read my collection of math used in our course, “REFRESHING High-School Mathematics”.
Use the equations for mechanical energy and work to show what is work and what is not. Make it clear why holding something off the ground or carrying something over a level surface is not work in the scientific sense.
The maximum work is done by a given force when it is along the direction of the displacement (cos \(\theta\) = ± 1), and zero work is done when the force is perpendicular to the displacement (cos \(\theta\) = 0).
