At a construction site, a helicopter is lifting two steel beams, each with a mas

Question

At a construction site, a helicopter is lifting two steel beams, each with a mass of 250 kg. One steel beam is attached directly to the helicopter by a cable. The second steel beam is not attached to the helicopter directly, but is instead hanging directly below the first steel beam and attached to the first beam by another cable. Assume the cables have no mass.

(a) If the steel beams are at rest, what is the tension in each cord?

Lowe cable--

upper cable(N)--

(b) If the steel beams are pulled upward with an acceleration of 1.70 m/s2 calculate the tension in each cable.

lower cable(N)--

upper cable(N)--

Explanation / Answer

(a)

If the steel beams are at rest, the tension in the upper cable:

Tupper = 2 m g = 2 ( 250 kg ) ( 9.8 m/s2) = 4900 N

Tension in the lower cable:

   Tlower = m g = ( 250 kg ) ( 9.8 m/s2) = 2450 N

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(b)

As it moves upward, the accleration would changes.

a + g = ( 1.7 m/s2 + 9.8 m/s2 ) = 11.5 m/s2

the tension in the upper cable:

Tupper = 2 m ( a+g ) = 2 ( 250 kg ) (  11.5 m/s2 ) = 5750 N

the tension in the lower cable:

Tlower = m ( a+g ) = ( 250 kg ) (  11.5 m/s2 ) = 2875 N

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