12. A car covers 40 km in first hour, 115 km in next two hours and 45 km in next one hour. Find out its average speed: a) 100 km/h b) 66.6 km/h c) 50 km/h d) none of these 13.Wind currents generated by uneven heating between the equator and the: a) moon b) poles c) sun d) stars 14. Smoke is hotter and lighter than: a) water b) heat c) air d) none of these 15. Who among the following was the first to observe that whenever air moves its pressure drop? a) Galileo b) Bernoulli c) Newton d) Einstein 16.An alternate name of natural disaster is: a) natural calamity b) storm c) cyclone d) tornado
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Explanation:
Letx consider, x= total distance covered by the car,
Time taken to complete the half distance with velocity v=40km/h,
t
1
=
2×40
x
=
80
x
hr. . . . .(1)
The time taken to complete another half distance with velocity u=60km/h
t
2
=
2×60
x
=
120
x
hr
The total time taken, t=t
1
+t
2
t=
80
x
+
120
x
=
48
x
hr
The average speed of the car,
v
avg
=
x/48
x
=48km/h
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