A train moves past a telegraph post and a bridge 264 m long in 8 seconds and 20 seconds respectively. What is the speed of the train?
A.69.5 km/hr
B.70 km/hr
C. 79 km/hr
D.79.2 km/hr
Answers
Answer:79.2
Length of the Bridge = 264 m.
Time taken to pass the bridge = 20 sec.
Time taken to passe the post = 8 sec.
Length of the train = X m (Let.)
To pass the bridge train need to cover Train's length + Bridge legnth (X +264).
Speed = Distance covered / time taken
Now,
X/8 = (264 + X)/20
20X = 264 *8 + 8X
20X - X = 264 *8
12X = 264 *8
X = (264 *8)/12
X = 176 m.
Speed of the train = 176/8 = 22 m/sec = (22*18)/5 = 79.2 Kmph
Step-by-step explanation:
let the length of the train = xm
a train crosses a telegraph post in 8 sec
● x/8 m/sec
to cross the bridge the train covers it own distance + the bridge
= ● x + 264 /20 m/sec
We know that ,
speed = distance/ time
=> x/8 = 264+ x /20
=> 20x = {8( x+ 264 )}
=> 20x = 8x + 2112
=> 12x = 2112
=> x = 176m
- 176/8 = (22 × 18/5 ) km /hr
- 79.2 km /hr