DC Machine

An electric vehicle requires a starting torque of 300Nm to accelerate at an appropriate rate from rest. The battery voltage of the vehicle is 240VDC and the motor is a series type. From the following information derive the motor parameters and the torque and emf constants:
(1). At start up the motor takes a current of 120A. At a speed of 1500 rpm the torque is 42 Nm
(2). Calculate the efficiency of this motor at 500 rpm and at 1500 rpm