Question: A guy can swim at a speed of 4.0 km/h in still water. How long does it take him to traverse a 1.0 km wide river at 3.0 km/h while keeping his strokes parallel to the current? After he reaches the opposite bank, how far down the river does he go?
Sol:
Speed of the guy = 4 km/h and width of the river = 1 km
Therefore, the time is taken to cross the river = Width of the river / Speed of the river
= 1/4 h
= 1/4 × 60 = 15 minutes
The Speed of the river, vr is equal to 3 km/h
Thus, distance covered with flow of the river = vr × t
= 3 × 1/3 = 1/4
= 3/4 × 1000 = 750 m
Question: If the horizontal range of a projectile is 4 times the maximum height attained by it, then the angle of projection is:
Options:
(a) 450
(b) 300
(c) 600
(d) 150
Answer: (a)
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