Physics Homework: A bead on wire

[Elliott98]

Homework Statement

A bead slides on a wire, which is in a vertical plane, as shown in the diagram. Gravity acts in the -y direction. The bead starts at A, moving to the right with an initial velocity v. The wire is frictionless between A and D and between F and G, but there is friction between D and F. (For each statement select True, False, Greater than, Less than, Equal to, or Not enough information to tell.http:////d2vlcm61l7u1fs.cloudfront.net/media%2F62f%2F62f71b78-00b4-43a8-a92b-de3a1b48521b%2Fphp3BwzEE.png
http:////d2vlcm61l7u1fs.cloudfront.net/media%2F87b%2F87b2fab7-a0ac-403b-89aa-426164f8224c%2Fphp6TF9ue.png

Homework Equations

KE= (1/2)mv^2
PE = mgh

The Attempt at a Solution

a) The bead is sliding down with gravity with no friction, so the speed will increase. Answer = True?

b) The velocity of the bead at D is higher than at F because before D, there is no friction, but after D to F, Friction is present. Because the velocity is smaller at F than D, the KE is smaller at F than at D. Answer = Greater than?

c) There is no friction present and its a horizontal surface so speed remains constant form D to E. Answer = Equal?

d) Conservation of energy. Answer = Equal

I'm not sure if these are correct. Any help would be greatly appreciated. Thanks![/B]

 

[kuruman]

Hi Elliott98 and welcome to PF.

We cannot see the statements that are supposed to be True or False. The pictures did not load. Try reloading them or perhaps you can enter them by hand.

 

[haruspex]

The velocity of the bead at D is higher than at F because before D, there is no friction, but after D to F, Friction is present.

What else might affect the velocity over that segment? Would the speed at F be the same as at D if there were no friction in between?

 

[Elliott98]

Hi Elliott98 and welcome to PF.

We cannot see the statements that are supposed to be True or False. The pictures did not load. Try reloading them or perhaps you can enter them by hand.

I can't seem to be able to upload them so here they are:

a) Between A and B, the speed increases.
b) The bead's kinetic energy at D is ... it's kinetic energy at F.
c) The speeds at D and E are equal.
d) The total energy of the bead at B is ... the total energy at D.

 

[kuruman]

a) Correct.
b) Think again in view of @haruspex's post#3.
c) Correct.
d) Correct.

 

[SammyS]

I can't seem to be able to upload them so here they are:

a) Between A and B, the speed increases.
b) The bead's kinetic energy at D is ... it's kinetic energy at F.
c) The speeds at D and E are equal.
d) The total energy of the bead at B is ... the total energy at D.

Actually, the preferred way to post is with text rather than images of textual material.

Also, it's helpful to post full size images, so here is the one image of yours that survived - now in full size.

and your answers ...

a) The bead is sliding down with gravity with no friction, so the speed will increase. Answer = True?

b) The velocity of the bead at D is higher than at F because before D, there is no friction, but after D to F, Friction is present. Because the velocity is smaller at F than D, the KE is smaller at F than at D. Answer = Greater than?

c) There is no friction present and its a horizontal surface so speed remains constant form D to E. Answer = Equal?

d) Conservation of energy. Answer = Equal

 

[SammyS]

a) Correct.
b) Think again in view of @haruspex's post#3.
c) Correct.
d) Correct.

For (c): There is friction in that segment.

 

[Elliott98]

For (c): There is friction in that segment.

Oops, I made a mistake. Thanks for pointing it out.

So I have a) True
b) Sorry, I'm a bit confused. The formula for kinetic energy is = 1/2 mv^2. So that mass at D is the same as at F so that doesn't change. For velocity, it will decrease because of friction? Or the velocity will increase because the beed is going down the slope, but friction will work against it so it will remain the same?
c) False, (because there is friction, the bead will slow down, so the speeds aren't equal)
d) Equal to.

Thanks for all the help!

 

[jbriggs444]

b) Sorry, I'm a bit confused. The formula for kinetic energy is = 1/2 mv^2. So that mass at D is the same as at F so that doesn't change. For velocity, it will decrease because of friction? Or the velocity will increase because the beed is going down the slope, but friction will work against it so it will remain the same?

You seem to be listing two possibilities there. Can you think of a third? (or a fourth).