A car travels from X to Y with uniform speed v_u and returns with uniform speed v_d. The average speed for the entire round trip is:

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NEET Physics QUESTION #7305

Question 1

A car travels from X to Y with uniform speed $v_u$ and returns with uniform speed $v_d$. The average speed for the entire round trip is:

Correct Answer Explanation

Let distance X to Y $= d$. Total distance $= 2d$.

Total time $= \dfrac{d}{v_u} + \dfrac{d}{v_d} = d\cdot\dfrac{v_u + v_d}{v_u v_d}$

Average speed $= \dfrac{2d}{d\cdot\dfrac{v_u+v_d}{v_u v_d}} = \mathbf{\dfrac{2v_u v_d}{v_u + v_d}}$ (harmonic mean)