A motorboat going downstream overcame a raft at a point A. One hour later it turned back and after sometime passed the raft at a distance 12 km from the point A. Find the river velocity (in km/hr) assuming the speed of the motorboat to be constant.

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Solution

Let angle velocity of motorboat be v

From the given figure $(v + u) t_{1} = u (t_{1} + t_{2}) + (v - u) t_{2} \Rightarrow t_{2} = t_{1}$ = 1 hr

But 12 km = $u (t_{1} + t_{2})$ so $u = \frac{12 k m}{2 h r}$ = 6 km/hr

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A motorboat going downstream overcame a raft at a point A. One hour later it turned back and after sometime passed the raft at a distance 12 km from the point A. Find the river velocity (in km/hr) assuming the speed of the motorboat to be constant.

Let angle velocity of motorboat be v From the given figure (v+u)t1=u(t1+t2)+(v−u)t2⇒t2=t1 = 1 hr But 12 km =u(t1+t2) so u=12km2hr = 6 km/hr

Let angle velocity of motorboat be v

From the given figure $(v + u) t_{1} = u (t_{1} + t_{2}) + (v - u) t_{2} \Rightarrow t_{2} = t_{1}$ = 1 hr

But 12 km = $u (t_{1} + t_{2})$ so $u = \frac{12 k m}{2 h r}$ = 6 km/hr