Motion in a Plane - Result Question 49

52. A stone is tied to a string of length 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

[2004]

(a) 2g

(b) 2(u2g)

(c) u2g

(d) uu22g

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Answer:

Correct Answer: 52. (b)

Solution:

  1. (b) Wmg=ΔK

mg=1/2mv21/2mu2

or, mv2=m(u22g]

or, v=u22gj^

u=ui^

vu=u22gj^ui^

|vu|=[(u22g)+u2]1/2=2(u2g)



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