Question

a compact car has a mass of 800kg and its efficiency is rated 18%(that is 18% of the available fuel energy is delivered to the wheels)find the energy required to accelarate the car from rest

Answer 1

Let's denote the target speed with $v$. Then, at this speed the kinetic energy of the car will be:

$$K = \dfrac{mv^2}{2}$$

where $m = 800 kg$ is a mass of the car. Since its efficiency is rated $18\% = 0.18$, then the energy, required to accelarate the car from rest to the speed $v$ is:

$$E = \dfrac{K}{0.18} = \dfrac{5mv^2}{18}[J]$$

One can substitute any required speed $v$ in m/s into the last expression and obtain the numerical result.

Answer. $E = \dfrac{5mv^2}{18} [J]$