Question: How do I calculate the power delivered to the motor using Ohm's Law?

[truettct]

1. Homework Statement

The battery has 1.35 V output voltage and 0.15 Ohm internal resistance. The battery is used to boot a small electric motor with 285 Ohm resistance. Find the power delivered to the motor. What the power will be if we use two batteries of this type in series?



3. The Attempt at a Solution

I thought the formula to use was

P_L=V_B²-(R_L/(R_i+R_L)²)

R_i= internal resistance
V_B²=output voltage
R_L=resistance

When I use this formula my answer is .00639W which is incorrect.
And I'm not sure how to do the second part of the problem

Any help on what I am messing up on would be appreciated.

Thanks

 

[vk6kro]

Don't look for complex formulae. This is pure Ohm's Law stuff.

The total resistance across the 1.35 Volts of the single battery is what?

(The internal resistance plus the motor resistance. They are in series.)

So, what current flows?

The motor has this current flowing in it and a known resistance, so what is the power delivered to the motor?

Now put another battery in series with the first one and do it again.