Question

Police start chasing a thief at 11 am and they caught him at 3.5 pm. If the speed of police is 90 km/h, calculate the speed of the thief. Initially, the thief was 45 km away from the police.

1. 80 km/h
2. 85 km/h
3. 100 km/h
4. 105 km/h

Answer 1

Correct Answer - Option 1 : 80 km/h

Given:

Speed of police = 90 km/h

Distance = 45 km

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:

Time taken by police = 3.5 pm – 10 am = 4.5 h

Distance covered by the police in

Let the speed of the thief is S km/h.

Relative speed = 90 – S km/h

⇒ 90 – S = 45/4.5

⇒ 90 – S = 10

⇒ S = 80 km/h

∴ The speed of the thief is 80 km/h.