An electric toy car with a mass of 3 kg is powered by a motor with a voltage of 4 V and a current supply of 7 A. How long will it take for the toy car to accelerate from rest to 4 m/s?

1 Answer
Jun 7, 2017

I got $0.86 s$

Explanation:

In reaching $4 \frac{m}{s}$ the car will have a Kinetic Energy of:
$K = \frac{1}{2} m {v}^{2} = \frac{1}{2} \cdot 3 \cdot {4}^{2} = 24 J$

The Power deliverd by the motor is:

$P = V I = 4 \cdot 7 = 28 W$ that means that it delivers $28 J$ each second.

The toy car will need $24 J$ so using a proportion we get:

$1 \text{sec":28J=x"sec} : 24 J$

or

$x = \frac{24}{28} = 0.857 \approx 0.86 s$