A train running at a uniform speed passes a bridge of 300 m long and 15 seconds and another Bridge 450 m long and 21 seconds find the speed of the train in kilometre per hour and the length of the train in metre
Answers
Answer:
75 m, 25 km/hr
Step-by-step explanation:
Let the speed of the train be 's' and length of train be 'l'.
∴ Speed = (Distance)/Time
(i) Passes a bridge of 300 m in 15 seconds:
s = (l + 300)/15
(ii) Passes another bridge 450 m in 21 seconds:
s = (l + 450)/21
From (i) & (ii), we get
⇒ (l + 300)/15 = (l + 450)/21
⇒ 21(l + 300) = 15(l + 450)
⇒ 21l + 6300 = 15l + 6750
⇒ 6l = 450
⇒ l = 75
∴ Length of the train = 75 m.
Substitute l = 75 in (i), we get
⇒ s = (l + 300)/15
= (375)/15
= 25.
∴ Speed of the train is 25 km/hr.
Hope it helps!
1. the length of the train:
2. the speed of the train in km/hr.
:
Let t = length of the train in meters
Let s = the speed of the train in meters/sec
:
write a speed equation for each bridge: Speed = dist/time
:
s = %28%28t%2B275%29%29%2F15
and
s = %28%28t%2B425%29%29%2F21
therefore
%28%28t%2B275%29%29%2F15 = %28%28t%2B425%29%29%2F21
Cross multiply
21(t+275) = 15(t+425)
:
21t + 5775 = 15t + 6375
:
21t - 15t = 6375 - 5775
6t = 600
t = 100 meters is the length of the train
:
Find the speed
s = %28%28100%2B275%29%29%2F15
s = 375%2F15
s = 25 meter/sec
:
Convert to km/hr:
S = %28%283600%2A25%29%29%2F1000
S = 90 km/hr