Physics - Circular Motion Question with Solution | TestHub

Speed increases uniformly means $\frac{dv}{dt}=$ constant, so $a_t$ is constant in magnitude.
But the tangential direction keeps changing, so ${\vec{a}}_t$ is not a constant vector; the centripetal acceleration $\frac{v^2}{R}$ grows with $v$.
The angular acceleration $\alpha =\frac{a_t}{R}$ is constant in magnitude AND direction (along the fixed axis), so it is the constant quantity.