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) $0,\ 6$
Concept. Average velocity $=$ displacement / time; average speed $=$ distance / time, both over the whole stated interval.
Step 1. Timeline. To the library: $\dfrac36 = 0.5$ h. Back: $\dfrac39 = \dfrac13$ h. She is home after $50$ min and rests for $10$ min.
Step 2. Average velocity. Displacement $= 0$, so $0$.
Step 3. Average speed. Distance $6$ km in $1$ h: $6$ km/h.
Answer. $0,\ 6$ (Option B).
Solution by Sreeraj P, M.Sc Physics