If a train is accelerating at a rate of 4km per hour per second and its initial velocity is 20km per hour what is its velocity after 30 seconds?

The train's velocity after 30 seconds can be calculated using the formula: final velocity = initial velocity + (acceleration * time). Plugging in the values, final velocity = 20 km/hr + (4 km/hr/s * 30 s) = 20 km/hr + 120 km/hr = 140 km/hr. So, the train's velocity after 30 seconds is 140 km/hr.