How will the armature current and the output power of a dc shunt motors change with increasing load?

With increasing torque load the armature tends to slow down; the motor draws more current to compensate, and if there is armature resistance the back emf generated by the armature falls to allow the increased current to flow, which causes the motor to settle at a lower speed.

The mechanical output power is the speed times the torque, and increasing the torque increases the power output provided the speed does not drop much.