Q 11-02-021NEETJEE MainMedium
A student walks $3$ km along a straight road from home to a library at $6$ km/h. Finding it closed, she immediately walks back home at $9$ km/h and then rests. Over the first $60$ minutes after leaving home, her average velocity and average speed (in km/h) are respectively
Answer: (B) $0,\ 6$
Time to the library: $\dfrac{3}{6} = 0.5$ h $= 30$ min. Time back: $\dfrac{3}{9} = \dfrac{1}{3}$ h $= 20$ min.
She is back home after $50$ min and rests for the remaining $10$ min.
In $60$ min: displacement $= 0$, so average velocity $= 0$.
Distance $= 3 + 3 = 6$ km in $1$ h, so average speed $= 6$ km/h.
(The resting time counts: averages are always over the stated interval.)
Solution by Sreeraj P, M.Sc Physics