A stone is tied to a string of length l and is whirled in a vertical cir...

Q. A stone is tied to a string of length l and is whirled in a vertical circle with the other end of the string as the centre. At a certain instant of time, the stone is at its lowest position and has a speed u. The magnitude of the change in velocity as it reaches a position where the string is horizontal (g being acceleration due to gravity) is

Description :

Aipmt Neet 2004 | WPE Q 3 | In this case Mechanical energy will remain conserved because tension will always act perpendicular to displacement i.e direction of velocity so its work done will be zero. Gravity is a conservative force and there is no non-conservative force present .

Conservation of Mechanical Energy

The work-energy theorem, shows that the change DKE in a body’s kinetic energy is equal to the net work done on it :
 DKE = Wnet
Consider separately the work Wc done by conservative force and the work Wnc done by nonconservative forces. Then
DKE = Wc+ Wnc
We’ve defined the change in potential energy DU as the negative of the work done by conservative forces. So we can write
DKE = – DU + Wnc
or DKE + DU = Wnc
We define the sum of the kinetic and potential energy as the mechanical energy. Then Equation shownthat the change in mechanical energy is equal to the work downe by non-conservative forces.
i.e. DE = Wnc
D \E = 0 if Wnc= 0
Thus if work done by non-conservative forces is zero the mechanical energy of the system is unchanged.
This called law of conservation of mechanical energy. It may also be written as
DU + DK E = 0
or DU = – DKE
or U + K E = constant
or Uin + K Ein = Uf + K Ef

We will take initial position at lowest position , where speed is given as ‘ u ‘ and final position where string will be perpendicular to vertical.

Don't forget to LIKE , SHARE & SUBSCRIBE my Channel.

Please Press BELL icon to receive latest updates.

Don't miss Hint based videos / concept related videos/ twisted qus videos available only on this channel , from which you can learn the most solid framework of problem solving/ clarity in application of different concepts/ formation of other problems with a small change in data given or language.

Check out text solution( No need to run videos all the time, solutions are available in written format)just a click away on

questionnahibanta.blogspot.com

 If you have anything to say/discuss ,feel free to contact Email :

questionnahibanta@gmail.com,    

If you want to be part of Exam related discussion/tips of

day with others Join me on Facebook page : Question Nahi Banta

You can also follow me on Instagram : questionnahibanta where you can share and find best exam related content.