8. In the preceding question, if the bob is
released from the horizontal position, what
will be its velocity at the lowest position?
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11th
Physics
Work, Energy and Power
Conservation of Energy
The bob of a pendulum is re...
PHYSICS
The bob of a pendulum is released from a horizontal position A as shown in the figure. If the length of the pendulum is 1.5m, what is the speed with which the bob arrives at the lower most point B, given that it dissipated 5% of its initial energy against air resistance?
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ANSWER
At the point A, the energy of the pendulum is entirely PE. At point B, the energy of the pendulum is entirely KE. It means that as the bob pendulum lowers from A to B, PE is converted into KE. Thus, at B, KE=PE. But 5% of the PE is dissipated against air resistance.
KE at B=95% of PE at A ....(i)
∴ From equation (i),
2
1
mv
2
=
100
95
mgh
v
2
=2×
100
95
gh=2×
100
95
×9.8×1.5
v=
10
19×9.8×1.5
=
27.93
=5.285ms
−1
v=5.3ms
−1
.