Final answer:
Accelerating torque is the torque generated by the rotor to accelerate the motor, and it appears as a positive, increasing value on a torque-time chart.
Step-by-step explanation:
Accelerating torque is the torque that is generated to increase the rotational speed of an object. Specifically, it refers to torque that results in changing the angular velocity over a period of time, which is essentially accelerating a rotation. On a torque-time chart, accelerating torque is usually shown as a positive value that increases over time until the desired angular velocity is reached.
In the context of motors, option A, torque generated by the rotor to accelerate the motor, is correct. The rotor is the part of the motor that actually rotates, so it makes sense that the accelerating force is generated there. If we look at a diagram, such as Figure 10.31 referenced in your question, counterclockwise rotations (seen from overhead) denote the positive direction of the torque.
The equation for the magnitude of torque is t = rF sin θ, where r is the lever arm, F is the force applied, and θ is the angle between the force vector and the lever arm. It's essential to remember that the effectiveness of this force in producing angular acceleration is maximal when the force is applied perpendicularly to the lever arm at a 90-degree angle (θ = 90°).