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sumit

· started a discussion

· 1 Months ago

Q63: In solution part, why we need to take underroot? (Question: 121647.0 )

concept says:

{Speed(A) x Time taken by A } = {Speed(B) x Time taken by B }

Speed(A) x (36/7) = 54 x (64/7)

Speed(A) = [{54 x (64/7)}/(36/7)]

[Note: Why we need to take under root here, it contradicts the solution given here.}

Question:

Two trains A and B left towards each Other from two different stations. After crossing each other, both trains A and B reached their destination within 5\(\cfrac{1}{7}\) h and 9\(\cfrac{1}{7}\)h respectively. If the speed of train B is 54 km/h, then find out the speed of train A.

Options:
A) 81 km/h
B)

65 km/h 


C) 60 km/h
D) 72 km/h
E) None of these
Solution:
Ans: (d)

Let the speed of Train A = SA and time taken by Train A = 5\(\cfrac{1}{7}\) h

Speed of Train B = 54 km/h and time taken by Train B = 9\(\cfrac{1}{7}\) h


SA= \(\cfrac{8 × 54}{6}\) =72 km/h

Knowledge Expert

· commented

· 1 Months ago

If two trains (or bodies) start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then:

(A's speed) : (B's speed) = (square root of b : square root of a)
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