Counter emf generated in a motor at full speed

[lloyd21]

Homework Statement

An electric motor draws 20.0 A of current when first switched on. The motors windings have a resistance of 5.0 ohm. Once the motor is up to full speed it draws only 4.4 A of current. Calculate the counter emf generated in the motor at full speed

Homework Equations

I = V/R
V=IR

The Attempt at a Solution

R = 5.0 ohm
A1 = 20.0 A
A2= 4.4 A n

1. (20A)(5.0ohm) = 100 V

2. (4.4A)(5.0ohm) = 22V

3. 100V - 22V = 78V

Im told I am missing some "change", however I think this is correct, it is change in voltage?

 

[andrevdh]

Looks fine to me.