RoganSarine
Nov3-09, 01:27 AM
Basically my instructor is confusing the heck out of me because I highly dislike how this course is structured. I dislike how in this specific chapter we are not taught:
\SigmaW = \DeltaEnergy
However, using this equation and my previous knowledge I can't seem to get the right answer in the following problem unless I assume there is no \DeltaPE which isn't true since \Deltaheight = .150
When using the relationship you see below, do we assume that the Work done by gravity doesn't exist since we compensate for it under the change in potential energy?
1. The problem statement, all variables and given/known data
In Figure 7-32, a constant force of magnitude 82.0 N is applied to a 3.00 kg shoe box at angle f = 53.0°, causing the box to move up a frictionless ramp at constant speed. How much work is done on the box by when the box has moved through vertical distance h = 0.150 m??
2. Relevant equations
http://www.lowellphysics.org/beta/Textbook%20Resources/Chapter%207.%20Kinetic%20Energy%20and%20Work/Problems/c07x7_11.xform_files/nw0314-n.gif
\SigmaW = \DeltaEnergy
\SigmaW = \DeltaKE + \DeltaPE
Wg + Wapp = 0(constant speed) + \DeltaPE
Wg + Wapp = \DeltaPE
3. The attempt at a solution
Using the above formula:
Wg + Wapp = \DeltaPE
Wg + Wapp = (3)(g)(\Deltaheight)
Wg + Wapp = (3)(g)(-.15)
Wg + Wapp = -4.4145
Wg = F * d * cos\Phi
Wg = mg * (.15) * cos(0)
Wg = (3)(9.81) * (.15)
Wg = 4.4145
Wapp = F * d * cos\Phi
Wapp = 82cos53 * (.15) * cos0
Wapp = 7.4
This relationship doesn't make any sense...
4.41 + 7.4 \neq -4.4145
Basically, if I assume that there is no change in potential energy, however, the answer does end up coming out right... kinda of.
\SigmaW = \DeltaEnergy
However, using this equation and my previous knowledge I can't seem to get the right answer in the following problem unless I assume there is no \DeltaPE which isn't true since \Deltaheight = .150
When using the relationship you see below, do we assume that the Work done by gravity doesn't exist since we compensate for it under the change in potential energy?
1. The problem statement, all variables and given/known data
In Figure 7-32, a constant force of magnitude 82.0 N is applied to a 3.00 kg shoe box at angle f = 53.0°, causing the box to move up a frictionless ramp at constant speed. How much work is done on the box by when the box has moved through vertical distance h = 0.150 m??
2. Relevant equations
http://www.lowellphysics.org/beta/Textbook%20Resources/Chapter%207.%20Kinetic%20Energy%20and%20Work/Problems/c07x7_11.xform_files/nw0314-n.gif
\SigmaW = \DeltaEnergy
\SigmaW = \DeltaKE + \DeltaPE
Wg + Wapp = 0(constant speed) + \DeltaPE
Wg + Wapp = \DeltaPE
3. The attempt at a solution
Using the above formula:
Wg + Wapp = \DeltaPE
Wg + Wapp = (3)(g)(\Deltaheight)
Wg + Wapp = (3)(g)(-.15)
Wg + Wapp = -4.4145
Wg = F * d * cos\Phi
Wg = mg * (.15) * cos(0)
Wg = (3)(9.81) * (.15)
Wg = 4.4145
Wapp = F * d * cos\Phi
Wapp = 82cos53 * (.15) * cos0
Wapp = 7.4
This relationship doesn't make any sense...
4.41 + 7.4 \neq -4.4145
Basically, if I assume that there is no change in potential energy, however, the answer does end up coming out right... kinda of.