A mass m is attached to a thin wire and whirled in a vertical circle . ...
A mass m is attached to a thin wire
and whirled in a vertical circle . The wire is most likely to break when
AIPMT/NEET 2019 | W.P.E Q 4
| 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
On applying formula of Tension force at any angle in string , we get
to know its a function of cosine
function which will has a maximum value when string makes an angle of zero with
vertical i.e at lowest position so if you have the right info then its an easy
qus,
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