Correct Answer - Option 1 :
18 min
Given:
Speed of thief = 9 km/h
Speed of policeman = 12 km/h
Formula Used:
Speed = Distance/Time
Concept Used:
If two objects are moving in the same direction with speeds S1 and S2,
Their relative speed is S1 – S2
Calculation:
Only the thief runs for 6 minutes.
Distance covered by the thief = 9 × 5/18 × 6 × 60 m = 900 m
Relative speed = 12 – 9 = 3 km/h
⇒ 3 × 5/18 m/s
⇒ 5/6 m/s
Time to catch the thief = Time required to cover 900 = 900/(5/6) s
⇒ 900/5 × 6 s
⇒ 180 × 6 s
⇒ (180 × 6)/60 = 18 min
∴ The policeman will catch the thief in 18 min.