An electric toy car with a mass of 2 kg is powered by a motor with a voltage of 3 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?

Jul 17, 2017

The time is $= 0.11 s$

Explanation:

The power is

$P = U I$

The voltage is $U = 3 V$

The current is $I = 7 A$

The power is

$P = U I = 3 \cdot 7 = 21 W$

The kinetic energy of the car is

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

The mass is $m = 2 k g$

The speed is $v = \frac{3}{2} m {s}^{-} 1$

so,

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

Let the time $= t s$

$E = P t$

$t = \frac{E}{P} = \frac{2.25}{21} = 0.11 s$

Jul 17, 2017

t= 0,107 s

Explanation:

the final kinetic energy of the car is ${E}_{K} = \frac{1}{2} m {v}^{2} = \frac{1}{2} 2 k g \times {\left(1 , 5 \frac{m}{s}\right)}^{2} = 2 , 25 J$
the power supplied is $P = V \times I = 3 V \times 7 A = 21 W$
since P=E/t you have $t = \frac{E}{P} = \frac{2 , 25 J}{21 W} = 0 , 107 s$