Circular MotionHardBloom L3
Question
On a train moving along east with a constant speed v, a boy revolves a bob with string of length on smooth surface of a train, with equal constant speed v relative to train. Mark the correct option(s).
Options
A.Maximum speed of bob is 2 v in ground frame.
B.Tension in string connecting bob is $\frac{4mv^{2}}{\mathcal{l}}$ at an instant.
C.Tension in string is $\frac{mv^{2}}{\mathcal{l}}$ at all the moments.
D.Minimum speed of bob is zero in ground frame.
Solution
Sol. Circular motion is in train's frame. In this frame sped v is constant.
${\overrightarrow{v}}_{bob,ground} = {\overrightarrow{v}}_{b,T} + {\overrightarrow{v}}_{T}$
vmax = v + v = 2v
vmin = –v + v = 0
$T = \frac{mv^{2}}{\mathcal{l}}$
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