Question

10. A car covers a distance X in 20s while moving
at a speed of 55 km h-. It covers a distance Y in
30s with a speed of 50kmh-!. Find (a) the total
distance covered by the car, and (b) average
speed of the car.​

Answer 1

Answer:

(a) 722.3 m

(b) 14.5 ms-1 or  52.2kmh-1

Explanation:

ANSWER FOR (a)

speed : 55kmh-1 → ms-1

= 55 × 5/18

= 15.28 ms-1

s = v × t

= 15.28 × 20

= 305.6  m

Therefore, X = 305.6 m

speed : 50 kmh-1 → ms-1

= 50 × 5/18

= 13.89 ms-1

s = v × t

= 13.89 × 30

= 416.7 m

Therefore, Y = 416.7 m

Total distance covered by car :

305.6 + 416.7 = 722.3 m

ANSWER FOR (b)

average speed = total distance covered ÷ total time taken

v = s ÷ t

= (722.3) ÷ (20 + 30)

= 14.5 ms-1

or 52.2 kmh-1

as 14.5 × 18/5 = 52.2 kmh-1

Answer 2

Explanation:

This is because tfie water as well as ink particles (molecules) are in continuous random motion. Due to motion, the blue coloured particles of the ink spreads all over and give blue colour to the water