NEET Solved Paper 2017 Question 29
Question: Preeti reached the metro station and found that the escalator was not working. She walked up the stationary escalator in time $ t _1. $ On other days, if she remains stationary on the moving escalator, then the escalator takes her up in time $ t _2. $ The time taken by her to walk up on the moving escalator will be
Options:
A) $ t _1-t _2 $
B) $ \frac{t _1+t _2}{2} $
C) $ \frac{t _1t _2}{t _2-t _1} $
D) $ \frac{t _1t _2}{t _2+t _1} $
Show Answer
Answer:
Correct Answer: D
Solution:
Velocity of girl w.r.t. elevator $ =\frac{d}{t _1}=v _{ge} $ Velocity of elevator w.r.t. ground $ v _{eG}=\frac{d}{t _2} $ then velocity of girl w.r.t. ground
$ \vec{v}{= _{gG}}={{\vec{v}} _{ge}}+{{\vec{v}} _{eG}} $ i.e, $ v _{gG}=v _{ge}+v _{eG} $ $ \frac{d}{t}=\frac{d}{t _1}+\frac{d}{t _2} $ $ \frac{1}{t}=\frac{1}{t _1}+\frac{1}{t _2} $ $ t=\frac{t _1t _2}{(t _1+t _2)} $
