Solve a Simple Physics Problem: Boat Speed and River Flow in 30 Minutes

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To solve the problem of a boat moving upstream against a river current, the boat's speed in still water is 30 km/hr, while the river's flow is 6 km/hr. The effective speed of the boat upstream is calculated as 30 km/hr - 6 km/hr, resulting in 24 km/hr. To determine the time taken to travel 12 km upstream, the formula time = distance/speed is applied, leading to a time of 30 minutes. The discussion emphasizes the importance of understanding relative velocities in this context.
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Homework Statement


A boat can move at 30 km/hr in still water. how long will it take to move 12 km upstream in a river flowing 6.0 km/hr.

I know the answer is 30 min but the way my teacher explained it is very difficult to remember can someone show me another way to do this problem?

the way she showed us:
Vbg = 30 km/hr
Vbr = Vbg + Vgr = 24 km/hr = 0.4 km/min
Vrg = 6.0 km/hr
Vgr = -6.0 km/hr + 12/0.4 = 30 min
 
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Do you agree that adding the velocity of the boat relative to the water + velocity of the water = velocity of the boat relative to ground (ie: net velocity) ?
 
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