Question

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

• A. $4J$
• B. $0.04J$
• C. $6J$
• D. $0.06J$

Answer 1

The correct option is D

$0.06J$

Step 1: Given data:

The blocks are uniform cubes of side $=2cm$

Mass of block $=0.1kg$

Step 2: Calculate the work done,

Total work done change in kinetic energy and change in potential energy. As there is no motion, thus, change in kinetic energy is zero.

The potential energy is :

$$\begin{gathered} \Rightarrow P.E=mg∆h \\ \Rightarrow P.E\left(block1\right)=0.1\times 10\times 0=0J \\ \Rightarrow P.E\left(block2\right)=0.1\times 10\times \frac{2}{100}=0.02J \\ \Rightarrow P.E\left(block3\right)=0.1\times 10\times \frac{4}{100}=0.04J \end{gathered}$$

Thus, the total potential energy is,

$\Rightarrow TotalP.E=0+0.02+0.04=0.06J$

Hence, option D is the correct answer.