Question

The current in an electromagnet connected to a 240-V line is 17.5 A . Part A At what rate must cooling water pass over the coils if the water temperature is to rise by no more than 7.50 ∘C ? The specific heat of water is 4186 J/(kg⋅∘C). Express your answer using three significant figures.

mt =_____ kgs

Answer 1

First find out the apparent power of the electric circuit.

This is -  

P = VI = 240*17.5 W = 4200 W = 4200 J/s = 4.2 kJ/s

Now this power will cause heating in the circuit.

The heat generated by the circuit will be carried
away by the flowing water.

Since water has a specific heat capacity of:
C = 4186 J/kg -C = 4.186 kJ/kg -C, then the heat absorbed by
water will be: Q = mCΔT

And, since the water is flowing at a rate: (m/t)
P = dQ/dt = (m/t)CΔT = (m/t)*(4.186 kJ/kg-C)*7.50

(m/t) = 4.2 / (4.186x7.50) = 0.1338 kg/s

In three significant figures, the answer is -

m/t = 0.134 kg/s.

Please note that you have asked the answer in mt (kgs) and this is not possible. Because when you ask about the rate then this must be in the form of kg/s.