# An electric toy car with a mass of 4 kg is powered by a motor with a voltage of 2 V and a current supply of 7 A. How long will it take for the toy car to accelerate from rest to 2 m/s?

Mar 5, 2017

$0.54 s$

#### Explanation:

The energy supplied is calculated by

$E = \frac{1}{2} m {v}^{2} = \frac{1}{2} \times 4 \times {2}^{2} = 8 J$

Electrical power is

$P = I V$

and mechanical power is

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

so we can say that

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

The question is asking for $t$, so rearrange

$t = \frac{E}{I V} = \frac{8}{2 \times 7} = 0.54 s$