A trolley containing water has total mass of 4000 kg and is moving at a speed of 40 m/s. Now water starts coming out of a hole from the bottom of the trolley at the rate of 8 kg/s. Speed of trolley after 50 s is
A
44.4 m/s
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B
40 m/s
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C
64 m/s
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D
54.44 m/s
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Solution
The correct option is A44.4 m/s Given that, Initial mass of water (m1)=4000 kg Initial velocity of trolley v1=40 m/s Rate of water coming out from the hole (mr)=8 kg\s Total mass of water flown out after (m3)50 s=8 kg\s×50 s ⇒m3=400 kg The direction of water coming out from the trolley is vertically downward. The momentum of the system in horizontal direction will not change. Initial momentum in horizontal direction = Final momentum in horizontal direction. m1v1=(m1−m3)v2 4000×40=(4000−400)v2 (v2= velocity of trolley after 50 s ) v2=44.44m/s