# An electric toy car with a mass of 3 kg is powered by a motor with a voltage of 7 V and a current supply of 1 A. How long will it take for the toy car to accelerate from rest to 5/3 m/s?

Mar 5, 2017

$0.6 s$

#### Explanation:

Electrical power is

$P = I V$

and mechanical power is

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

so

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

We can work out $E$ by

$E = \frac{1}{2} m {v}^{2} = \frac{1}{2} \times 3 \times {\left(\frac{5}{3}\right)}^{2} = 4.17 J$

Rearrange the equation for time, which we want to find:

$t = \frac{E}{I V} = \frac{4.17}{7 \times 1} = 0.6 s$