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NEET Physics QUESTION #7317
Question 1

A particle covers half its total distance with speed $v_1$ and the remaining half with speed $v_2$. Its average speed over the entire journey is:

  • $\dfrac{v_1+v_2}{2}$
  • $\dfrac{v_1 v_2}{v_1+v_2}$
  • $\dfrac{2v_1 v_2}{v_1+v_2}$✔️
  • $\dfrac{v_1^2 v_2^2}{v_1^2+v_2^2}$
Correct Answer Explanation

Let total distance $= 2d$.

Total time $= \dfrac{d}{v_1} + \dfrac{d}{v_2} = \dfrac{d(v_1+v_2)}{v_1 v_2}$

Average speed $= \dfrac{2d}{\dfrac{d(v_1+v_2)}{v_1 v_2}} = \mathbf{\dfrac{2v_1 v_2}{v_1+v_2}}$

(This is the harmonic mean of $v_1$ and $v_2$.)