Friction coefficient

What is the weight of a car when it moves on a horizontal road at a speed of v = 50 km/h at engine power P = 7 kW? The friction coefficient is 0.07

Correct answer:

m =  720 kg

Step-by-step explanation:

$$\begin{gathered} v=50\text{ km/h}\to \text{ m/s}=50\mathrm{/}3.6\text{ m/s}=13.88889\text{ m/s } \\ P=7000\text{ W } \\ t=0.07 \\ g=10{\text{m/s}}^2 \\ P=Fv \\ F=P\mathrm{/}v=7000\mathrm{/}13.8889=504\text{ N } \\ F=tmg \\ m=F\mathrm{/}(t\cdot g)=504\mathrm{/}(0.07\cdot 10)=720\text{ kg} \end{gathered}$$

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