# 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 result:

m =  720 kg

#### Solution:

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

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