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Work Done by Force of Gravity

A child build...

Question

A child builds a tower from three blocks. The blocks are uniform cubes of side $2 c m$ . The blocks are initially lying on the same horizontal surface and each block has a mass of $0.1 k g$ . The work done by the child is (in J)

4

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0.04

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6

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0.06

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Solution

The correct option is D $0.06$
Total work done is change in kinetic energy plus change in potential energy. Since, change in kinetic energy is zero. So total work done by child is change in potential energy of blocks.

Assuming center of mass of blocks initially is at 1cm level and value of g=10

Change in height of center of mass for-
Block 1- Zero
Block2- 1 cm to 3cm= 2cm
Block 3- 1cm to 5cm= 4cm

Potential energy is-
$E = m g △ h E (b l o c k 1) = 0.1 \times 10 \times 0 = 0 J E (b l o c k 2) = 0.1 \times 10 \times (\frac{2}{100}) = 0.02 J E (b l o c k 3) = 0.1 \times 10 \times (\frac{4}{100}) = 0.04 J A d d i n g a l l = 0 + 0.02 + 0.04 = 0.06 J$

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A child builds a tower from three blocks. The blocks are uniform cubes of side 2cm. The blocks are initially lying on the same horizontal surface and each block has a mass of 0.1kg. The work done by the child is (in J)

A child builds a tower from three blocks. The blocks are uniform cubes of side $2 c m$ . The blocks are initially lying on the same horizontal surface and each block has a mass of $0.1 k g$ . The work done by the child is (in J)