Three children, each of weight 361 N, make a log raft by lashing together logs of...

Three children, each of weight 361 N, make a log raft by lashing together logs of diameter 0.21 m and length 1.60 m. How many logs will be needed to keep them afloat in fresh water? Take the density of the logs to be 800 kg/m³.

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Here is what I solved before, please modify the figures as per your question. Please let me know if you have further questions. Ifthis helps then kindly rate 5-stars.

Three children, each of weight 356 N, make a log raft by lashing together logs of diameter 0.30m and length 1.80 m. How many logs will be needed to keep them afloat in fresh water? Take the density of logs to be 800 kg/m^3.

The buoyancy created by each log can be found by thedifference between the weight of a log and the weight of the samevolume of water... like this:
.
volume of a log = area * length = pi*r^2 L = pi * 0.15^2 * 1.80 = 0.127235 m3
.
mass of a log = density * volume = 800 *0.127235 = 101.79 kg
.
mass of same volume of water = 1000 *0.127235 = 127.235 kg
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difference in mass = 127.235 - 101.79 = 25.447 kg
.
difference in weight = mg = 25.447 * 9.80 = 249.38 Newtons
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Each log can support 249.38 N of weight. Thekids weigh 356 * 3 = 1068 N
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So they need 1068 / 249.38 = 4.28 logs... but they cant have afraction

5 logs

genius_generous answered 1 week ago

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