SOLUTION: the speed of a motor launch with respect to still water is 7m/s and the speed of stream is 3m/s . when the launch began travelling upstream , afloat was dropped from it . the launc

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Question 893009: the speed of a motor launch with respect to still water is 7m/s and the speed of stream is 3m/s . when the launch began travelling upstream , afloat was dropped from it . the launch travelled 4.2 km upstream , turned about andd caught up with the float . how long is it before the launch reaches the float??
Found 2 solutions by lwsshak3, Alan3354:
Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
he speed of a motor launch with respect to still water is 7m/s and the speed of stream is 3m/s . when the launch began travelling upstream , afloat was dropped from it . the launch travelled 4.2 km upstream , turned about and caught up with the float . how long is it before the launch reaches the float??
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speed of boat downstream=7+3=10 m/s*1000m/km*3600 sec/hr=36 km/hr
speed of boat upstream=7-3=4 m/s*1000m/km*3600 sec/hr=14.4 km/hr
speed of current=3 m/s*1000m/km*3600 sec/hr=10.8 km/hr
travel time=distance/speed
..
boat traveling upstream:
travel time=4.2/14.4
..
distance float traveled (downstream):
speed*travel time=10.8(4.2/14.4)=3.15 km
..
distance boat must travel (downstream)to catch float=4.2+3.15=7.35 km
travel time=7.35/36=0.20 hrs ≈12.25 min
..
how long is it before the launch reaches the float after turning around? 12.25 min

Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
the speed of a motor launch with respect to still water is 7m/s and the speed of stream is 3m/s . when the launch began travelling upstream , afloat was dropped from it . the launch travelled 4.2 km upstream , turned about andd caught up with the float . how long is it before the launch reaches the float??
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4.2 km = 4200 meters
Speed upstream = 7-3 = 4 m/sec
The boat travels away from the float for 4200/4 = 1050 seconds = 17.5 minutes
It takes the same time to get back to it.
The speed of the stream is not relevant.