# Two identical balls  and , each of mass 2 kg and radius , are suspended vertically from inextensible strings as shown in Fig. The third ball  of mass 1 kg and radius  falls and hits  and  symmetrically with 10 m/s. Speed of both  and  just after the collision is 3 m/s Speed of  just after collision is a) 2 m/s b)  m/s c) 5 m/s d)

## Question ID - 101124 :- Two identical balls  and , each of mass 2 kg and radius , are suspended vertically from inextensible strings as shown in Fig. The third ball  of mass 1 kg and radius  falls and hits  and  symmetrically with 10 m/s. Speed of both  and  just after the collision is 3 m/s Speed of  just after collision is a) 2 m/s b)  m/s c) 5 m/s d)

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Answer Key : (a) -

(a)

First calculate,  As the ball  and  are constrained to move horizontally (immediately after collision), if ‘ ’ be the impulse imparted by ball ‘ ’ to each of  and , the impulse received by ball  from them would be

Now, each of ball  and  received impulse ‘ ’ as shown in Fig., but moves horizontally as its vertical comp. gets balanced by impulse imparted to ball  and  by the respective strings and hence,

magnitude of impulse)

Now, for ball , if its final velocity is  downwards, we have

sign indicates that it is directed upwards)

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