# An electric toy car with a mass of 2 kg is powered by a motor with a voltage of 9 V and a current supply of 7 A. How long will it take for the toy car to accelerate from rest to 3/2 m/s?

Mar 5, 2017

$0.036 s$

#### Explanation:

Energy applied to the toy car is calculated as kinetic energy,

$E = \frac{1}{2} m {v}^{2} = \frac{1}{2} \times 2 \times {\left(\frac{3}{2}\right)}^{2} = 2.25 J$

We know that electrical power is

$P = I V$

and mechanical power is

$P = \frac{E}{t}$

so

$I V = \frac{E}{t}$

$t = \frac{E}{I V}$
$t = \frac{2.25}{9 \times 7} = 0.036 s$