A man rows at 6 km\/hr in still water and with the same effort he rows 4.5 km\/hr against the stream of a river. What is the speed if he rows (with the same effort) along the stream of the river?<\/p>\n
[amp_mcq option1=”7\u00bd km\/hr” option2=”7 km\/hr” option3=”6\u00bd km\/hr” option4=”6\u00bc km\/hr” correct=”option1″]<\/p>\n
Speed against the stream (upstream speed) = Speed in still water – Speed of stream = v – u.
\nWe are given that the speed against the stream is 4.5 km\/hr.
\nv – u = 4.5
\nSubstitute the value of v:
\n6 – u = 4.5
\nu = 6 – 4.5 = 1.5 km\/hr.
\nThe speed of the river stream is 1.5 km\/hr.<\/p>\n
We need to find the speed if he rows along the stream (downstream speed) with the same effort. The effort remaining the same means his speed relative to the water is still v.
\nSpeed along the stream (downstream speed) = Speed in still water + Speed of stream = v + u.
\nSubstitute the values of v and u:
\nDownstream speed = 6 + 1.5 = 7.5 km\/hr.<\/p>\n
The question asks for the speed in one of the given options. 7.5 km\/hr is equivalent to 7 and a half km\/hr. A man rows at 6 km\/hr in still water and with the same effort he rows 4.5 km\/hr against the stream of a river. What is the speed if he rows (with the same effort) along the stream of the river? [amp_mcq option1=”7\u00bd km\/hr” option2=”7 km\/hr” option3=”6\u00bd km\/hr” option4=”6\u00bc km\/hr” correct=”option1″] This question was previously … <\/p>\n
\n7.5 = 7 + 0.5 = 7 + 1\/2 = 7\u00bd km\/hr.
\n<\/section>\n
\n– Speed downstream = Speed in still water + Speed of stream.
\n– The effort remaining the same implies the speed of the man relative to the water (speed in still water) is constant.
\n<\/section>\n
\nSpeed in still water = (Downstream speed + Upstream speed) \/ 2
\nSpeed of stream = (Downstream speed – Upstream speed) \/ 2
\nIn this case, we found v=6 and u=1.5.
\nUpstream speed = 6 – 1.5 = 4.5 km\/hr (Given).
\nDownstream speed = 6 + 1.5 = 7.5 km\/hr (Calculated).
\nCheck using the formulas:
\nSpeed in still water = (7.5 + 4.5) \/ 2 = 12 \/ 2 = 6 km\/hr (Matches given v).
\nSpeed of stream = (7.5 – 4.5) \/ 2 = 3 \/ 2 = 1.5 km\/hr (Matches calculated u).
\n<\/section>\n","protected":false},"excerpt":{"rendered":"