Consider the following physical situations. Identify the forces which do work upon the indicated object (in boldface type) and categorize them as conservative or non-conservative forces. Then indicate whether the total mechanical energy of the object changes; it it changes, then indicate whether the change is a positive or negative change. Finally, indicate whether the potential energy and the kinetic energy changes; if PE or KE changes, then indicate whether the change is a positive or negative change. Description of Physical Situation Identity of Forces Which Do Work: Change in TME Change in PE Change in KE Conserv. Non- Conserv. Yes (+ or -) No Yes (+ or -) No Yes (+ or -) No a. A force is applied to move a physics cart from the floor to the top of an inclined plane at a constant speed. _________ _________ _____ _____ _____ _____ _____ _____ b. A physics student scurries up a flight of stairs at constant speed. _________ _________ _____ _____ _____ _____ _____ _____ c. In a moment of unsupervised phun, a physics student hoists herself onto a staircase banister and accelerates down the banister. Ignore all friction forces. _________ _________ _____ _____ _____ _____ _____ _____ d. A ball is dropped from rest from on the top of a hill and falls to the ground below. Ignore air resistance. _________ _________ _____ _____ _____ _____ _____ _____ e. A ball leaves top of a hill with a large horizontal velocity. It falls to the ground below. Ignore air resistance. _________ _________ _____ _____ _____ _____ _____ _____ f. A Hot Wheels car is at rest at an elevated position along an inclined plane; it is released and rolls to a position along the ground. Ignore air resistance. _________ _________ _____ _____ _____ _____ _____ _____ g. A Hot Wheels car is in motion at the bottom of a hill when it hits a computer diskette box and skids to a stop. _________ _________ _____ _____ _____ _____ _____ _____ h. A pendulum bob swings from its highest position to its lowest position. _________ _________ _____ _____ _____ _____ _____ _____ i. A physics cart is released from rest at an elevated position along an inclined plane; it is released and rolls to a position along the incline approximately 5 cm from the bottom. _________ _________ _____ _____ _____ _____ _____ _____
Kinematics
A machine is a device that accepts energy in some available form and utilizes it to do a type of work. Energy, work, or power has to be transferred from one mechanical part to another to run a machine. While the transfer of energy between two machine parts, those two parts experience a relative motion with each other. Studying such relative motions is termed kinematics.
Kinetic Energy and Work-Energy Theorem
In physics, work is the product of the net force in direction of the displacement and the magnitude of this displacement or it can also be defined as the energy transfer of an object when it is moved for a distance due to the forces acting on it in the direction of displacement and perpendicular to the displacement which is called the normal force. Energy is the capacity of any object doing work. The SI unit of work is joule and energy is Joule. This principle follows the second law of Newton's law of motion where the net force causes the acceleration of an object. The force of gravity which is downward force and the normal force acting on an object which is perpendicular to the object are equal in magnitude but opposite to the direction, so while determining the net force, these two components cancel out. The net force is the horizontal component of the force and in our explanation, we consider everything as frictionless surface since friction should also be calculated while called the work-energy component of the object. The two most basics of energy classification are potential energy and kinetic energy. There are various kinds of kinetic energy like chemical, mechanical, thermal, nuclear, electrical, radiant energy, and so on. The work is done when there is a change in energy and it mainly depends on the application of force and movement of the object. Let us say how much work is needed to lift a 5kg ball 5m high. Work is mathematically represented as Force ×Displacement. So it will be 5kg times the gravitational constant on earth and the distance moved by the object. Wnet=Fnet times Displacement.
Consider the following physical situations. Identify the forces which do work upon the indicated object (in boldface type) and categorize them as conservative or non-conservative forces. Then indicate whether the total mechanical energy of the object changes; it it changes, then indicate whether the change is a positive or negative change. Finally, indicate whether the potential energy and the kinetic energy changes; if PE or KE changes, then indicate whether the change is a positive or negative change.
Description of Physical Situation |
Identity of Forces
Which Do Work: |
Change in TME | Change in PE | Change in KE | ||||
| Conserv. | Non-
Conserv. |
Yes
(+ or -) |
No | Yes
(+ or -) |
No | Yes
(+ or -) |
No | |
|
a. A force is applied to move a physics cart from the floor to the top of an inclined plane at a constant speed. |
_________ | _________ | _____ | _____ | _____ | _____ | _____ | _____ |
|
b. A physics student scurries up a flight of stairs at constant speed. |
_________ | _________ | _____ | _____ | _____ | _____ | _____ | _____ |
|
c. In a moment of unsupervised phun, a physics student hoists herself onto a staircase banister and accelerates down the banister. Ignore all friction forces. |
_________ | _________ | _____ | _____ | _____ | _____ | _____ | _____ |
|
d. A ball is dropped from rest from on the top of a hill and falls to the ground below. Ignore air resistance. |
_________ | _________ | _____ | _____ | _____ | _____ | _____ | _____ |
|
e. A ball leaves top of a hill with a large horizontal velocity. It falls to the ground below. Ignore air resistance. |
_________ | _________ | _____ | _____ | _____ | _____ | _____ | _____ |
|
f. A Hot Wheels car is at rest at an elevated position along an inclined plane; it is released and rolls to a position along the ground. Ignore air resistance. |
_________ | _________ | _____ | _____ | _____ | _____ | _____ | _____ |
|
g. A Hot Wheels car is in motion at the bottom of a hill when it hits a computer diskette box and skids to a stop. |
_________ | _________ | _____ | _____ | _____ | _____ | _____ | _____ |
|
h. A pendulum bob swings from its highest position to its lowest position. |
_________ | _________ | _____ | _____ | _____ | _____ | _____ | _____ |
|
i. A physics cart is released from rest at an elevated position along an inclined plane; it is released and rolls to a position along the incline approximately 5 cm from the bottom. |
_________ | _________ | _____ | _____ | _____ | _____ | _____ | _____ |
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