determine max welding speed in a butt welding operation

Question

In butt welding operation on plates, the het input necessary is given by

Q = 8 K T_ct $(0.2+\frac{Vb}{4\alpha })$

Where K = thermal conductivity,

T_c= temp increases from room temp upto MP

t = thickness of plate,

V = welding speed,

b = width of weld, 

α = thermal diffusivity

Two alloy steel plates as shown in fig are to be welding using a power source rated at 5 kVA having a duty cycle of 75%. Using the given data, determine the maximum welding speed for the job given in mm/s

Data: K = 45 W/m⁰ C, T_c = 1450⁰C, and α = 1.2 x 10^–5 m²/s.

(a) 14.2                            (b) 19.0

(c) 1065                           (d) none