• # question_answer A uniform rectangular marble slab is 3.4 m long and 2.0 m wide. It has a mass of 180 kg. If it is originally lying on the flat ground, how much work is needed to stand it on an end? A) 2.0 kJ B) 3.0 J C) 3.0 kJ D) 3000 kJ

Solution :

[c] The work done by gravity is the work done, as if all the mass were concentrated at the centre of mass.   The work necessary to lift the object can be thought of as the work done against gravity and is just$W=mgh$, where h is the height through which the centre of mass is raised.   $W=180\left( 9.8 \right)\text{ }\left( 1.7 \right)=\text{ }3.0\text{ }kJ$

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