How fast is this bead traveling down the wire

  • Thread starter Thread starter Ronaldo21
  • Start date Start date
  • Tags Tags
    Bead Wire
AI Thread Summary
The discussion focuses on calculating the speed of a metal bead sliding down a friction-free wire under gravity, starting from rest. Participants emphasize using the conservation of energy principle, where gravitational potential energy at the top converts into kinetic energy as the bead descends. The maximum speed occurs at the lowest point, where potential energy is minimized. To find numerical speeds at various points (B, D, E), a reference level for potential energy must be established. However, without specific measurements for point C, a numerical answer cannot be determined for that location.
Ronaldo21
Messages
30
Reaction score
0
A big metal bead slides due to gravity along an upright frictiion-free wire. It starts from rest at the top of the wire as shown in the sketch. How fast is it traveling as it passes.

http://https://www.physicsforums.com/attachment.php?attachmentid=22509&stc=1&d=1260854052

Point B?
Point D?
Point E?
At what point does it have the maximum speed?
I got B for this because it goes down really fast.
 

Attachments

  • 359550b5-5e96-4bbe-b6f9-7940fb3e02ef.gif
    359550b5-5e96-4bbe-b6f9-7940fb3e02ef.gif
    6 KB · Views: 705
Last edited by a moderator:
Physics news on Phys.org


The way to do this question is to use conservation of energy.

Gravitational PE at top goes into PE + KE as the bead slides down.
 


so what do we exactly do?
because we don't have the number to d and e. i think i get b.
 


Ronaldo21 said:
so what do we exactly do?
because we don't have the number to d and e. i think i get b.

I think you might want to review the concept of conservation of energy for objects falling in a gravitational field. Briefly, you pick a reference level where potential energy = 0. When the object is above that level its PE is given by mgx where x is its current height. The conservation of energy equation goes as

Energy at the start = mgx + \frac{1}{2} m v^2

Here your energy at the start is mgh. Now look at your drawing carefully. Where IS the object going the fastest? This is subtle because it's where the PE is the LEAST. What is the relationship between points b, d, e? Which one is highest? Or they all at the same height?
 


hmm i think i get it so the answer will be some kind of formula then right??
 


Ronaldo21 said:
hmm i think i get it so the answer will be some kind of formula then right??

Actually you can get a numerical answer for the speed at points b, d, e if you pick your reference level (PE = 0, x = 0) along the horizontal line passing through b, d, e. You cannot get a numerical answer for point c because you don't know how far below point b it is.
 
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
I was thinking using 2 purple mattress samples, and taping them together, I do want other ideas though, the main guidelines are; Must have a volume LESS than 1600 cubic centimeters, and CAN'T exceed 25 cm in ANY direction. Must be LESS than 1 kg. NO parachutes. NO glue or Tape can touch the egg. MUST be able to take egg out in less than 1 minute. Grade A large eggs will be used.
Back
Top