Motion In A Straight Line Ques 50
50. A car covers the first half of the distance between two places at $40$ $ km / h$ and other half at $60$ $ km / h$. The average speed of the car is
[1990]
(a) $40 $ $km / h$
(b) $48 $ $km / h$
(c) $50 $ $km / h$
(d) $60 $ $km / h$
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Answer:
Correct Answer: 50.(b)
Solution:
- (b) Total distance $=s$;
Total time taken
$=\frac{s / 2}{40}+\frac{s / 2}{60}=\frac{5 s}{240}=\frac{s}{48}$
$\therefore$ Average speed $=\frac{\text{ total distance }}{\text{ total time }}$
$=\frac{s}{s / 48}=48$ $ km / h$
$v _{a v}=\frac{2 v_1 v_2}{v_1+v_2}=\frac{2 \times 40 \times 60}{40+60}=48$ $ km / h$
BETA
