A bumper consisting of two helical springs of circular section brings to rest a railway wagon of mass 1500 kg and moving at 1 m/s. While doing so, the springs are compressed by 150 mm. Then, the maximum force on each spring (assuming gradually increasing load) is:
(a) 2500 N (b) 5000 N
(c) 7500 N (d) 3000 N