The velocity-time graph of robber's car and a chasing police car are shown in the following graph. Police car crosses the robber's car in time   

detailed solution

Correct option is C

From graph, velocity of robber's car = 10 ms-1Let police car crosses it after t second.Distance travelled by robber's car = 10 t mPolice car is moving with a constant acceleration of 1 ms-2 as it attains a velocity of 10 ms-1 in 10 s after starting from rest. Distance travelled in t second = 12·a·t2 = 12t2When the police car crosses the robber's car, distance travelled by the both cars should be same from the startingpoint of chase.∴          12t2=10t⇒t=20 s