A body is moving unidirectionally under the influence of a source of constant power supplying energy. Which of the diagrams shown in the figure correctly shows the displacement-time curve for its motion?

1.   2.
3. 4.

Hint: Use dimensional analysis to find the relation between the distance and time.
 

Step: Identify the correct graph between the displacement-time curve.
For constant power
Displacement \(d \propto{t}^{3 / 2}\)
Because \({P}=\frac{\vec{F} \cdot d \vec{s}}{d t}=\vec{F} \cdot \vec{v}=~\text{constant}~~~(\because {P}=\text{constant according to the problem})\)
Now, will use dimensional analysis;
\({[{F}][{V}]=\text { constant }} \)
\(\Rightarrow\left[{MLT}^{-2}\right]\left[{LT}^{-1}\right]=\text { constant } \)
\(\Rightarrow {L}^2 {T}^{-3}=\text { constant }(\because \text { mass is constant }) \)
\(\Rightarrow {L} \propto{T}^{3 / 2}\)
\(\Rightarrow \text{displacemnt}~~d \propto{t}^{3 / 2}\) 

Hence, option (2) is the correct answer.