# An electric toy car with a mass of 15 kg is powered by a motor with a voltage of 8 V and a current supply of 3 A. How long will it take for the toy car to accelerate from rest to 4 m/s?

Mar 5, 2017

$t = 5 s$

#### Explanation:

Electrical power is given by

$P = I V$

and mechanical power by

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

so

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

We can calculate the kinetic energy, $E$, by

$E = \frac{1}{2} m {v}^{2} = \frac{1}{2} \times 15 \times {4}^{2} = 120 J$

$t = \frac{E}{I V} = \frac{120}{8 \times 3} = 5 s$