Question

An automobile starter rated at 2.25 hp draws how many amps from a 10.0 V battery?

Answer 1

First we need to convert the power from horsepower (hp) into watts. Since $1 hp=736 W$, we have
$P=2.25 hp \cdot 736 W/hp=1655 W$

Then we know that the electrical power of a device is the product between the voltage and the current:
$P=VI$
So if we re-arrange this equation, we get the current flowing in the circuit:
$I= \frac{P}{V}= \frac{1655 W}{10.0 V}=165.5 A$