Question

The motor in a toy car operates on$6.00V$, developing a$4.50V$back emf at normal speed. If it draws$3.00A$at normal speed, what current does it draw when starting?

Short answer

The current it draws when starting is $12A$.

Step-by-step solution

Definition of current and resistance 

Current is the term used to describe the speed at which charge moves. Resistance is the propensity of a substance to oppose the flow of charge.

Given information and Formula to be used

$\begin{array}{c}{I}_{back}=3A\\ V=6V\\ Backemf=4.50V\end{array}$

The current in a circuit,

$I=\frac{V}{R},$

where$V$is the potential and$R$is the resistance.

Calculating the current  

First we need find the resistance value,

$\begin{array}{c}{I}_{back}=\frac{V-Backemf}{R}\\ 3=\frac{6-4.5}{R}\\ R=0.5\mathrm{\Omega }\end{array}$

Now finding current it draws when starting,

$\begin{array}{c}I=\frac{V}{R}\\ I_{start}=\frac{V}{R}\\ I_{start}=\frac{6}{0.5}\\ I_{start}=12A\end{array}$

Therefore, current value is $12A$.