Figure 6-18: http://www.webassign.net/walker/06-18alt.gif(adsbygoogle = window.adsbygoogle || []).push({});

The pulley system in Figure 6-18 is used to lift a crate of mass m = 52 kg. Note that a chain connects the upper pulley to the ceiling and a second chain connects the lower pulley to the crate. Assume that the masses of the chains, pulleys, and ropes are negligible.

(a) Determine the force F required to lift the crate with constant speed.

N

(b) Determine the tension in each chain when the crate is being lifted with constant speed.

N (top chain)

N (bottom chain)

The answers in the back of the book are 260 N for part A and 510 N for part b for both chains.

The 510 part is easy. f=ma f=52*9.81 = 510. Each chain should have 510N of tension. No reason to divide it into half the tension for each chain.

But the first part? Where'd they get 260 from? Gravity is pulling down with f=ma or 510N. So if you don't pull the rope with at least 510N, you're not going to lift the box. Shouldn't 260N of force on the rope just put 260N of tension on the chains while not budging the box one bit? 260 is approximately but not exactly half of 510. I don't know if that yields a clue?

Anyone???

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# Homework Help: Tension and Force

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