A (trolley + child) of total mass 200 kg is moving with a uniform speed of 18 km/h on a frictionless track. The child of mass 20 kg starts running on the trolley from one end to the other (10 m away) with a speed of 10 ms^–1 relative to the trolley in the direction of the trolley's motion and jumps out of the trolley with the same relative velocity. What is the final speed (in m/s) of the trolley.