A boat travels at 12 km/h in still water, and the stream's speed is 3 km/h. If a boatman rows 90 km to a destination and comes back, how much time does he take in total?
A
9 hours
B
15 hours
C
16 hours
D
18 hours
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Question: A boat travels at 12 km/h in still water, and the stream's speed is 3 km/h. If a boatman rows 90 km to a destination and comes back, how much time does he take in total?
Solution:
Given,
Speed of the boat in still water = 12 km/h
Speed of the current = 3 km/h
Speed of the boat downstream = (Speed in still water + Speed of current) = (12 + 3) km/h = 15 km/h
Speed of the boat upstream = (Speed in still water − Speed of current) = (12 − 3) km/h = 9 km/h
Time taken to go downstream = Distance / Speed = (90/15) hours = 6 hours
Time taken to go upstream = Distance / Speed = (90/9) hours = 10 hours
Total time for the round trip = (6 + 10) hours = 16 hours
0
Updated: 5 days ago
A 120 meters long train is running at a speed of 108 km per hour. It will cross a railway platform 210 m long in-
Created: 2 weeks ago
A
11 sec
B
13 sec
C
15 sec
D
12 sec
Question: A 120 meters long train is running at a speed of 108 km per hour. It will cross a railway platform 210 m long in-
Solution:
Here,
Speed of the running train = 108 km/hr
= {108 × (5/18)} m/sec
= 30 m/sec
And length of the train is = 120 metres
Length of platform = 210 m
So, the time will taken by the train = (Length of train + Length of platform)/Speed
= (120 + 210)/30
= 330/30
= 11 sec
0
Updated: 2 weeks ago
Two trains are running in the same direction at 80 km/h and 60 km/h. The faster train crosses a man in the slower train in 36 seconds. What is the length of the faster train?
Created: 5 days ago
A
120 meters
B
140 meters
C
200 meters
D
220 meters
Question: Two trains are running in the same direction at 80 km/h and 60 km/h. The faster train crosses a man in the slower train in 36 seconds. What is the length of the faster train?
Solution:
Relative speed of train = (80 - 60) km/h
= 20 km/h
= (20 × 1000)/3600
= (50/9) m/s
∴ Distance covered = Speed × Time
= (50/9) × 36
= 200 meters
To overtake the person, the train has to travel a distance equal only to its own length.
So, Length of faster train = Distance covered = 200 meters.
0
Updated: 5 days ago
