# An electric toy car with a mass of 5 kg is powered by a motor with a voltage of 3 V and a current supply of 4 A. How long will it take for the toy car to accelerate from rest to 2 m/s?

Apr 30, 2018

The time is $= 0.83 s$

#### Explanation:

The power is

$P = U I$

$\text{Power"="Voltage"xx"Current}$

The voltage is $U = 3 V$

The current is $I = 4 A$

The power is

$P = U I = 3 \cdot 4 = 12 W$

The kinetic energy of the car is

$E = \frac{1}{2} m {v}^{2}$

The mass of the car is $m = 5 k g$

The speed is $v = 2 m {s}^{-} 1$

So,

The kinetic energy is

$E = \frac{1}{2} m {v}^{2} = \frac{1}{2} \cdot 5 \cdot {\left(2\right)}^{2} = 10 J$

Let the time $= \left(t\right) s$

$E = P t$

$\text{Energy=Power" xx "time}$

The time is

$t = \frac{E}{P} = \frac{10}{12} = 0.83 s$