Cubical blocks of mass m and side l are piled up in a vertical column.The total gravitational potential energy of a column of three blocks is
A) mgl.
B)3mgl.
C) mgl.
D)6mgl.
E)9mgl.

Question

Cubical blocks of mass m and side l are piled up in a vertical column.The total gravitational potential energy of a column of three blocks is
A) mgl. 
B)3mgl. 
C) mgl. 
D)6mgl. 
E)9mgl.

Quizplus · Accepted Answer

The gravitational potential energy of a block at height h is given by U = mgh, where m is the mass of the block, g is the acceleration due to gravity, and h is the height of the block. 
For the first block at the bottom of the column, its gravitational potential energy is U = mgl. 
For the second block, its height is 2l and its gravitational potential energy is U = mgh = mgl(2) = 2mgl. 
For the third block, its height is 3l and its gravitational potential energy is U = mgh = mgl(3) = 3mgl. 
Adding up the gravitational potential energies of all three blocks, we get 
U_total = 3mgl + 2mgl + mgl = 6mgl 
Therefore, the correct answer is C.

Cubical Blocks of Mass M and Side L Are Piled