Question

on a torque vs angular acceleration, graph should the y-intercept be zero? why?

Answer 1

From Newton's second law

comparing this equation with

We get

which is the y-intercept.

Now, we know that when a torque is applied to a system, the system undergoes an angular acceleration but when there is no torque, there must not be any angular acceleration.

In short, we know from Newton's first law that a system continues to be in the state it is until an external force/torque is applied. So, without torque, there is no angular acceleration.