How many people before it sinks

  • Thread starter superjen
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In summary, a raft made of 9 logs lashed together, each with a diameter of 29.1 cm and a length of 5.7 m, can hold people before their feet start getting wet. The average person has a mass of 69.3 kg and the density of water and wood is 1000 kg/m3 and 600 kg/m3, respectively. This can be calculated by comparing the upthrust of the logs (equal to the weight of water displaced) to the downforce of the logs and people combined.
  • #1
superjen
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A raft is made of 9 logs lashed together. Each is 29.1 cm in diameter and has a length of 5.7 m. How many people can the raft hold before they start getting their feet wet. Assume the average person has a mass of 69.3 kg and that the density of water and wood is 1000 kg/m3 and 600 kg/m3, respectively

All i know iss

FB = mpg + mrg
i don't really know how to figure it out from here!
 
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  • #2
A floating object displaces water equal to it's weight.
So how much mass of water would be displaced if the logs were completely submerged (hint volume of logs and density of water)
Now how much do those logs alone weigh - and so how much extra weight of people could be added.
 
  • #3
can you define your variables, it will help us to answer your question too? ie. what is FB and mpg and mrg?

Remember that the force of bouyancy is related to the volume of the liquid that is displaced.

Don't forget to find out the mass (and weight) of all the logs.

Drawing a diagram (Free body diagram) with force arrows will also help.
 
  • #4
mgb_phys beat me to it. :smile:
 
  • #5
People will start to get their feet wet when the logs are just underwater and the people aren't. So the upthrust due to the logs will be equal to the weight of the logs and of the people standing on them.

Upthrust = weight of water displaced = log volume * water density

DownForce = weight of logs + weight of people

Our condition is Upthrust = DownForce
 

FAQ: How many people before it sinks

How does the size of a ship affect its capacity to hold people before sinking?

The size of a ship can significantly impact its capacity to hold people before sinking. Larger ships have more space and are typically built to withstand greater weights, making them less likely to sink. However, even small ships can hold a large number of people if they are properly designed and maintained.

Is there a specific number of people that a ship can hold before it sinks?

There is no specific number of people that a ship can hold before it sinks. The number of people a ship can hold before sinking depends on various factors such as the size and design of the ship, the weight and distribution of the cargo, and the conditions of the water.

What are some factors that can cause a ship to sink when carrying people?

Some common factors that can cause a ship to sink when carrying people include overloading, structural damage, rough weather conditions, and human error. It is crucial for ships to be properly maintained and operated to ensure the safety of passengers.

Can a ship sink if it has lifeboats and life jackets for everyone on board?

Even if a ship has enough lifeboats and life jackets for everyone on board, it can still sink. These safety measures can help increase the chances of survival, but they cannot prevent a ship from sinking. It is important for ships to have proper safety protocols and emergency plans in place to minimize the risk of sinking.

How does the weight distribution of a ship affect its ability to hold people without sinking?

The weight distribution of a ship plays a crucial role in its ability to hold people without sinking. If the weight is unevenly distributed, it can cause the ship to become unstable and increase the risk of capsizing or sinking. Proper loading and distribution of cargo are essential for maintaining the stability of a ship and preventing it from sinking.

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