EK # 242 and 245

[rhinovirus722]

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EK 242.
A 100 kg man dangles a 50 kg mass from the end of a rope. If he stands on a frictionless surface and hangs the mass over a cliff with a pulley, the tensions in the rope will be?
a. 250
b. 333
c. 500
d. 667

Answer is B.

Here it is apparent that mg=ma + t (due to acceleration). The man is accelerating to the edge of the cliff due to tension thus t=ma for him. If you combine the systems you get T+T/2=mg. It has been a long day can some one take this farther to get the answer maybe I am missing something.

However what actually prompted me to write this post was question 245

EK 245
Background:
The masses below hang across a massless, frictionless pulley. what is the tension in the rope. ( The diagram has a pulley with a rope on it that has a mass m on one side and a mass 2m on the other)
Question
As the masses become infinitely large, the tensions in the rope becomes
a. 0N
b. 500N
c. 1000N
d. infinite

The answer is C. However, I would have thought that it would be infinite because the tension in the rope would be between 2mg and mg and if you increase the value of m you would therefore increase the tension unless there is a catch. Can some one also explain this...

 

[collegestud2013]

242.

a = F/M = 50 kg(10 m/s^2)/(50 kg + 100 kg) = 3.33 m/s^2

T = m(g - a) = 50 kg(10 m/s^2 -3.33 m/s^2) = 333 N

 

[SN2ed]

Thread moved. These types of questions belong in the Study Q&A forum.

 

[jissho]

Bump. Anyone care to take a shot at EK physics 245.

 

[ilovemcat]

Bump. Anyone care to take a shot at EK physics 245.

That question is referencing question 242. There was a typo in the book.