a) 0.04 km/s
b) 0.03 km/s
c) 0.05 km/s
d) 0.02 km/s
Answer: b
Explanation:
Let their speeds be x m/sec and y m/sec respectively.
$$\eqalign{
& \frac{{1200}}{{x + y}} = 15 \cr
& \Rightarrow x + y = 80…..(i) \cr} $$
$$\eqalign{
& \frac{{1200}}{{x – y}} = 60 \cr
& \Rightarrow x – y = 20…..(ii) \cr} $$
Adding (i) and (ii),
2x = 100 or x = 50
Putting x = 50 in (i), we get : y = 30
Speed of slower plane :
= 30 m/sec
= 0.03 km/sec
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