Question

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`?

Answer 1

The time is `=0.11s`

Explanation:

The power is

`P=UI`

The voltage is `U=3V`

The current is `I=7A`

The power is

`P=UI=3*7=21W`

The kinetic energy of the car is

`E=1/2mv^2`

The mass is `m=2kg`

The speed is `v=3/2ms^-1`

so,

`E=1/2*2*(3/2)^2=2.25J`

Let the time `=ts`

`E=Pt`

`t=E/P=2.25/21=0.11s`

Answer 2

t= 0,107 s

Explanation:

the final kinetic energy of the car is `E_K = 1/2 mv^2 = 1/2 2 kg xx (1,5 m/s)^2= 2,25 J`
the power supplied is `P= V xx I=3 V xx 7A = 21 W`
since P=E/t you have `t = E/P = (2,25J)/ (21 W) = 0,107 s`