Physics, 10.03.2020 02:07 manny2085

Alvin paddled for 2 hours with a 8-km/h current to reach a campsite. The return trip against the same current took 10 hours. Find the speed of the boat in still water.

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Answer from: angelaisthebest1700

The speed of the boat in still water is 12km/h.

Explanation:

This is a relative motion problem. The boat is moving relative to the water, which is moving relative to the ground. We can express this with the formula:

$v_{b/0}=v_{b/w}+v_{w/0}$

Where $v_{b/0}$ is the speed of the boat relative to the ground, $v_{b/w}$ is the speed of the boat relative to the water, and $v_{w/0}$ is the speed of the water relative to the ground.

We have that $v_{w/0}=8km/h$ and that, in the first trip $v_{b/0}=\frac{x}{2h}$ and in the second trip $v_{b/0}=\frac{x}{10h}$ , where x is the distance traveled. Also, in the first trip $v_{b/w}$ and $v_{b/0}$ are positive and in the second one are negative (because the boat goes in opposite directions). So, using some mathematics, we can say that:

$\frac{x}{2h} =v_{b/w}+8km/h; -\frac{x}{10h} =-v_{b/w}+8km/h\\\\x=2h(v_{b/w}+8km/h);x=-10h(-v_{b/w}+8km/h)\\\\\implies 2h(v_{b/w}+8km/h)=-10h(-v_{b/w}+8km/h)\\\\-4v_{b/w}=-48km/h\\\\v_{b/w}=12km/h$

This means that the speed of the boat relative to the water is 12km/h. This is independent to the speed of water, so the speed of the boat in still water is 12km/h.

Answer from: Quest

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.

Answer from: Quest

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me

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