Two trains each of length 100 m are...
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Two trains each of length 100 m are running on parallel tracks. One overtakes the other in 20 s when they are moving in the same direction and crosses the other in 10 s when they move in the opposite directions. The velocities of the two trains are (1) 15 m/s & 5 m/s (2) 25 m/s & 15 m/s (3) 10 m/s & 10 m/s (4) 30 m/s & 10 m/s

NEET/Medical Exams
Physics
Solution
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( bullet ) Let ( u & v ) be the velocity of the two trains named ( A & B ). While overtaking the relative velocity of train A with respect to ( mathrm{B}=mathrm{u}-mathrm{v} ). While crossing, the relative velocity of train A with respect to ( B=u+v ). - Total distance to be travelled by Train A while crossing ( =100+100= ) 200 So, ( 20=200 div u-v ) ( Rightarrow mathrm{u}-mathrm{v}=10 ldots .1) ) ( mathrm{AlsO} ) ( 10=200 div u+v ) ( Rightarrow mathrm{u}+mathrm{v}=20 ldots ldots .2) ) ( bullet ) On solving the equation ( 1 & 2, ) we get; ( bullet * ) ( mathrm{u}=15 mathrm{M} / mathrm{S} ) of the train ( mathrm{A} / ) First Train. ( mathrm{v}=5 mathrm{M} / mathrm{S} ) of the train ( mathrm{B} / mathrm{Second} ) Train.
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