Physics 163

Unit 5: Work, Energy and Power

Problem Set A

Overview:

Problem Set A targets your ability to use basic equations of work, energy and power in order to analyze physical situations and determine unknown quantities.

Work:

When a force acts upon an object to cause a displacement of the object, then it is said that work is done. Work is dependent upon the amount of force, the amount of displacement, and the angle between the force and displacement vector.

W = F • d • cos

By taking the angle into account, the equation only considers the amount of the force which is responsible for causing the displacement. When a force acts perpendicular to the displacement, the angle is 90 degrees and the force does no work upon the object. The standard meteric unit of work is the Joule; 1 Joule is equivalent to a Newton • meter.

Power:

Power is the rate at which work is done on an object. It is a time-based quantity. The equation for power takes into account both work and time.

P = W / t

The standard meteric unit of power is the Watt; 1 Watt is equivalent to a Joule / second.

Energy

There are two forms of mechanical energy - kinetic energy and potential energy. Kinetic energy is defined as the energy of motion possessed by an object; it is dependent upon mass and speed.

Potential energy is the energy stored by an object as a result of its position. In this problem set, we will be concerned about gravitational potential energy which is dependent upon mass and the object's vertical position or height.

The equations for kinetic energy (KE) and potential energy (PE) are stated below.

 KE = 0.5 • m • v2 PE = m • g • h

The total mechanical energy possessed by an object is the sum of the kinetic and potential energy.

You will have to master the above concepts and use the equations to be successful in Problem Set A. Additionally, you will need to be able to:

• convert units from non-standard metric form to standard metric form.
• utilize the equation for the force of gravity in situations in which an object is being lifted at constant speed.
• practice the habits of a good problem-solver.

One Final Caution:

This problem set only test your conceptual understandings in addition to you mathematical abilities. It is common in many of the problems that extraneous numerical values will be stated in the problem description; such values do not need to be used in the solution. This extraneous information will be a distraction primarily to students who treat physics problems as mere exercises in mathematics. Without an understanding of the above relationships, you will be tempted to force such information into your calculations. Physics is about conceptual ideas and relationships; and problem sets test your conceptual understanding of these relationships. If you treat this problem set as a mere exercise in the algebraic manipulation of physics equations, then you are likely to become frustrated quickly. As you proceed through this problem set, be concepts-minded. Do not strip physics of its conceptual meaning.

View Sample Problem Set.

 Problem Description Audio Link 1 Work calculation 2 Use of work equation to determine displacement 3 Work calculation for a lifting motion 4 Work calculation 5 Work calculation; similar to a lab done in class 6 Work calculation for a lifting motion; attention to units is critical 7 Power calculation for a lifting motion; similar to a lab done in class 8 Complex power calculation 9 Straight-forward kinetic energy calculation 10 Use of kinetic energy equation to determine the speed of an object 11 Potential energy calculation; attention to units is critical 12 Determinatin of TME from height, speed and mass information 13 Determinatin of TME from height, speed and mass information; attention to units is critical 14 Potential energy calculation

Audio Help for Problem: 1 || 2 || 3 || 4 || 5 || 6 || 7 || 8 || 9 || 10 || 11 || 12 || 13 || 14

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