Tuesday, 2 October 2007 - 6:36 PM EDT

Name: "Giovanna"

2 I don't think that centripetal force can do work because it is a net force and it is the other forces that are acting on the object.

3 What dose work mean in this situation? Is it moving an object on it's own or just contribution to the motion as a whole? I guess that in the second sense it does do some work. On inclines, it acts against gtravity and decreases the net force. I'm really not sure about this one.

25 The work on the suitcase is equal to the force parallel to the motion times the total distance. That means that the path would affect the work because the distance is greater. Time would only affect work as far as it affects the distance. Height and weight would both affect the situation because they are the distanceand the force.

Tuesday, 2 October 2007 - 10:34 PM EDT

Name: "Bob"

2. since centripetal force is only a concept and not an actual force, it cannot do work on an object.

3.  The normal force can indeed do work on an object. Take for instance a rising elevator. The normal force that the elevator exerts on you as it rises up is more than  the force of gravity on you downward, so the normal force does work lifting you up some distance.

25. The amount of work you do depends only on the height of the table since Work equals fore multiplied by displacement. The mass has no impact on the work done, and taking a complicated path up to that table top still produces the same displacement. The time it takes is only used when calculating power, which has no application here.

Tuesday, 2 October 2007 - 10:38 PM EDT

Name: "Matt Hazzard"

2. No a centripetal force cannot do work on an object because the displacement of the object is 0, so in W=fd cos 0(theta) if d, the displacement is 0, then the whole thing is 0 meaning no work.

 3. An elevator is an example of a situation where the normal force is doing work.  The elevator is moving up so the normal force from the floor of the elevator has to do work on you to keep you moving up with the object.

25. It depends on A, C, and D.  A because using a series of ramps would require more work because you would need to exert a larger force due to friction between the suitcase and the ramps.  C because the higher the table the more displacement and in W=fd cos0 if you increase d you increase the work.  And D because if you increase the weight you increase the amount of force needed to move the object.  And if you increase the force you increase the amount of work.

Tuesday, 2 October 2007 - 10:46 PM EDT

Name: "MB Kellett"

2) I don't think the centripetal force can do work because work is parallel to the displacement. In circular motion, the movement is not parallel to the displacement therefore, no work is done.

3) I'm not positive but I think the normal force can do work when the object's motion is upwards.

25) Work = force (dispacement) cos theta. Therefore the time it takes doesn't matter. That only comes into play when you're talking about power. The height of the table matters because that effects the displacement, and the weight of the suitcase matters because it alters mg, altering the force needed to lift it. The complexity of the path doesn't matter because displacement is still the same.

Tuesday, 2 October 2007 - 10:58 PM EDT

Name: "Jonathan Hellmer A.K.A. 64 oz."

1.  Centripital force cannot do work on an object since displacement is 0 meaning that there would be no work because the work equation would equal 0.

 2. Normal force can do work on an object because if you take the example of an elevator force is going in the direction of the normal force meaning that work has to be done by the normal force to get the object moving which means that it does work because it also has to  overcome the force of gravity to move.

3. If you lift a suitcase the height, the weight of the suitcase, and a more complicated path will all increase the work done.  The higher you have to raise the object the more work you have to do because you would increase the displacement making you have to do more work.  The weight of the suitcase would cause more work because by increasing the force which is mg more work would have to been done too. Finally, a more complicated path would create more work because if for example you use a ramp to get the suitecase up to the table you have to do more work to overcome an additional force which would be the force of friction.

Wednesday, 3 October 2007 - 12:03 AM EDT

Name: "Chris Addis"

2. Centripetal force cannot do work on an object because it really isn’t a new force it just means that a net force is acting on a object and that the net force is directed toward the center. Also the fact that when you have centripetal force it implies that the object is moving in a circle and therefore it means that it is displacement or d is zero. So that means that work is zero since the formula for work is W = F*D*Cosine theta.

 

3. An example of normal force doing work is when an elevator is going up. Think about what forces are acting on you get into an elevator. The only force acting on you when the elevator is stationary is the normal force of the elevator and your force of gravity. When the elevator starts to move upward the normal force of the elevator floor has to exert a force on you to make you move upward with the elevator. 

 

25. A) I think that it dose take more work if you do in fact take a complicated path then if you just go straight up. For example if you were to take a zigzag path in lifting a suitcase then you would have to worry about the your x and y displacement. While if you were just to take a straight-line path then you only have to worry about the y displacement. So in the zigzag path you would have to add your works together and in a straight-line path you just have the one. B) Time does matter when it come to the work needed to lift a suitcase since the formula for work is w = F*D*Cosine theta. C) The height of the table will cause more work because your displacement or d will change based on the height of the table. D) The weight of the suitcase will cause more work because it will take a greater or less force or f to lift up that suitcase.

Wednesday, 3 October 2007 - 8:52 AM EDT

Name: "Special Relativity"

Centripetal force does not do work on an object because it is always perpendicular to an objects motion.  Also, if work is force over a distance, it doesn't really make sense to say that centripetal force does work ver a distance if the force is always perpendicular to the objects motion.

 The normal force can do work.  For example, in an elevator moving upward, the normal force of the floor does work on the passangers to lift them to a higher altitude. 

If one is lifting a suitcase, the amount of work done on the suitcase only depends on the final height and the weight of the suitcase.  Gravity is a conservative force, unlike friction, so the path taken does not impact the amount of work done.  Also, the time that it takes to move the suitcase does not matter either.  Work is a force over a distance, not a force over time.  Force over time is impulse

Wednesday, 3 October 2007 - 8:55 AM EDT

Name: "Jon Hellmer"

Hey Guys,

It was a pretty tough game last night.  We ended up losing 3 to 1, but we played hard.  Strath Haven was a good team and I am just getting ready for Thursday when we play Harriton.  The season isn't over yet boys, so let's keep winning!!!

Wednesday, 3 October 2007 - 10:32 AM EDT

Name: "Joe Mahon"

Centripetal force cannot do work on an object because it is a net force not a actual force. Normal force however can do work on an object because constant forces produce work and the normal force is a constant force. Work is not affected by the path taken or the amount of time it takes. However work is affected by the height of the table when lifting a suitcase and it is also affected by the weight of the suitcase.

Wednesday, 3 October 2007 - 9:39 PM EDT

Name: "D. Wilson - 64 oz."

2. Centripetal force cannot do work for two reasons.  One is that centripetal force itself is not a force, it just means there is a net force acting on an object causing it to move in a circle.  Also, centripetal force is always perpendicular to the motion of the object which would make the amount of work zero.

3. The normal force can do work in a few situations.  One of these situations would be an elevator.  The normal force of the floor is the force that makes you move upwards.

25. The amount of work is force over a distance, therefore, the path you take does not matter.  Also, the time doesn't matter for the same reason.  The height of the table does matter though as well as the mass of the suitcase as they would affect the distance and the force, respectively.

Thursday, 11 October 2007 - 2:10 PM EDT

Name: "anonymous"

2) no, work is Fdcosθ, since θ is always 90 with centripetal force since it moves tangent to the circular path, work is always 0

 

3) no, since normal force can never move an object, it cant do work, setting d equal to 0, therefore Fdcosθ would be zero.

 

25)      a. no, it doesn’t matter if you take a curved path since horizontal motion in the air doesn’t require force.

b. no, work doesn’t account for time, that would be power

c. yes, this is the distance in the work equation

d. yes, this determines the force it takes to lift the suitcase from the ground

Thursday, 11 October 2007 - 2:12 PM EDT

Name: "Dave"

that was me by the way, sorry i didn't post my name