Motion in a Straight Line - Result Question 8

8. 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

(a) $40 km / h$

(b) $48 km / h$

(c) $50 km / h$

(d) $60 km / h$

[1990]

Topic 2: Non-uniform motion

Show Answer

Answer:

Correct Answer: 8. (b)

Solution:

  1. (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 $=\frac{\text{ total distance }}{\text{ total time }}$

$=\frac{s}{s / 48}=48 km / h$

$v _{a v}=\frac{2 v_1 v_2}{v_1+v_2}=\frac{2 \times 40 \times 60}{40+60}=48 km / h$



NCERT Chapter Video Solution

Dual Pane