A train takes 50 sec to cross a boy travelling at 6 km/h in the opposite direction to it. Another train which is half as long as and 25% faster take 30 sec to cross the stationary pole. Find the approximate length of the second train.
বিকল্পসমূহ (নিজের উত্তর যাচাই করতে ক্লিক করুন):
সঠিক উত্তর
1 (125 m)
বিস্তারিত ব্যাখ্যা ও বিশ্লেষণ:
Solution:
Let m be the length of the first train.
Let r be the speed of the first train in meters per second.
then m=50(r+5/3m/s).
Let n be the length of the second train. Since the second train is half as long as the first train we know that n=1/2m.
Let 1.25r be the speed of the second train.
The length of the second train is n = 30 ×1.25r Since n=1/2m
we can substitute to make 1/2m=30 × 1.25r.
Or m = 2 × 30 × 1.25r = 75r.
m =75r.
We can now combine the 2 equations:
50(r+5/3) = 75r
50r+250/3=75r
150r+250=225r
75r=250
r =10/3.
m =75r = 75 × 10/3 = 250 meters.
The second train is 125 meters long.
