A thief running at speed of 'x' km/h is chased by a policeman running at a speed of 10 km/h. If the thief is ahead by 100 metres, the policeman catches the thief after 3 minutes. At what speed is the thief running ('x' being the unknown speed)?
Answer & explanation
Correct answer: option 2
Distance to cover by policeman = 100 m
Time taken to catch the thief = 3 minutes = 180 sec
Relative speed = ( 10 - x ) km/h
Relative speed = \(\frac{100}{180 }\) m/sec
x m/sec = x ×(\frac{18}{5 }\) km/h
= \(\frac{100}{180 }\)×(\frac{18}{5 }\)
= 2 km/h
Now ,
10 - x = 2
x = 8 km/h
So , speed of thief is 8km/h