Q104 / 200 · NEET 2007 · Physics

A car moves from $\mathrm{X}$ to $\mathrm{Y}$ with a uniform speed $v_u$. The average speed for this round trip is :

  • A
    $\sqrt{v_u v_d}$
  • B
    $\frac{v_d v_u}{v_d+v_v}$
  • C
    $\frac{v_u+v_d}{2}$
  • Correct answer
    D
    $\frac{2 v_d v_u}{v_d+v_u}$

Solution

Average speed $\begin{aligned} & =\frac{\text { Total distance }}{\text { Total time }} \\ & =\frac{2 d}{\frac{d}{V_u}+\frac{d}{V_d}}=\frac{2 V_d V_u}{V_d+V_u} \end{aligned}$

Hence, the correct answer is option: 'D'.

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