Forty 2 kg blocks 20.0 cm thick are used to make a wall. Each row of the wall will contain 10 blocks. The first block is placed at the reference level. How much gravitational potential energy is stored in the wall when the blocks are set in place?

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The wall is made of forty 2.0 kg blocks each 20 cm thick. They are arranged in 4 rows one on top of the other each with 10 blocks.

One row can be considered to be a single object of mass 10*2 = 20 kg. The height of the row is how high the center of the block is from the reference. For the first row this is 10 cm, for the second it is 30 cm, for the third it is 50 cm and the final row is at a height of 70 cm. The gravitational potential energy stored is 20*9.8*(10 + 30 + 50 + 70) = 31360 J

The gravitational potential energy stored in the blocks of the wall is 31360 J

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