Chapter 23 - Magnetic Flux and Faraday's Law of Induction - Problems and Conceptual Exercises - Page 831: 42

$257rpm$

We know that $\epsilon_{max}=NBA\omega$ $\implies \frac{\epsilon_{max1}}{\omega_1}=NBA=\frac{\epsilon_{max2}}{\omega_2}$ $\implies \omega_2=\frac{\epsilon_{max2}}{\epsilon_{max1}}\omega_1$ We plug in the known values to obtain: $\omega_2=\frac{55}{45}(210rpm)=257rpm$