A man of \( 60 \, \text{kg} \) is running on the road and suddenly jumps into a stationary trolly car of mass \( 120 \, \text{kg} \). Then, the trolly car starts moving with velocity \( 2 \, \text{m}\,\text{s}^{-1} \). The velocity of the running man was ________ \( \text{m}\,\text{s}^{-1} \), when he jumps into the car.