A train running at a certain speed crosses another train running in the opposite direction in 4.8 seconds. to find out the speed of the first train , which of the following information P and Q is sufficient ?
P : Then length of the first train Q : The length of the second train
Answer : Option E
Let two trains of lengths a and b metres be moving in opposite directions at u m /s and v m/s
Time taken by he trains to cross each other = `(a + b)/(u + v)` sec
`:.` `(a + b)/(u + v)` = 4.8
In order to find u, we must know a, b and v,
i.e. , length of first train , length of second rain and the speed of the second train .
Thus , P and Q are not sufficient .
`:.` The correct answer is (E) .
A train running at a certain speed crosses a stationary engine in 20 seconds . to fine out the speed of the train which of the following information is necessary ?
Answer : Option D
Time taken by the train o cross a stationary engine
= (Length of train + Length of engine ) /( Speed of the train )
`rArr ` (Length of train + Length of engine ) /( Speed of the train ) = 20 ( given)
Hence , to find the speed of the train , the length of the train and the length of the engine both must be known.
`:.` The correct answer is (D).
Two trains, one from Howrah to Patna and the other from Patna to Howrah , start simultaneously . After they meet , the trains reach their destinations after 9 hours and 16 hours. respectively . The ratio of heir speeds is :
Answer : Option B
Let us name he trains as A and B . then ,
(A's speed) : (B's speed )
`sqrt(b)` : `sqrt(a)` = `sqrt(16)` : `sqrt(9)` = 4 : 3.
A train X starts from Meerut at 4 p.m. and reaches Ghaziabad at 5 p.m. while anther rain y starts from Ghaziabad at 4 p.m. and reaches Meerut at 5.30 p.m. The two trains will cross each other at
Answer : Option A
Suppose , the distance between Meerut and Ghaziabad is `x` km.
Time taken by X to cover `x` km = 1 hour.
Time taken by Y to cover `x` km = `3/2` hours.
`:.` speed of X = `x` kmph ,
Speed of Y = `((2x)/(3))` kmph
Let them meet y yours after 4 p.m. , hen
`xy + (2xy)/(3) = x hArr y(1 + 2/3) = 1 hArr y = 3/5 ` hours
= `(3/5 xx 60)` min = 36 min.
So, the two trains meet at 4.36 p.m.
Two stations A and B are 110 km apart on a straight line One train starts from A at 7 a.m and travels towards B at 20 kmph , Anther train starts from B at 8 a.m. and travels towards A at a speed of 25 kmph . At what time will they meet ?
Answer : Option B
Suppose they meet `x` hours after 7 a.m.
Distance covered by A in `x` hours = 20 `x` km.
Distance covered by B in `(x - 1)` hours = 25`(x - 1)` km
`:.` ` 20 x + 25 (x - 1) = 110 hArr 45x = 135 hArr x` = 3
So , they meet at 10 a.m.