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fishingspree2
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Homework Statement
The 4 wheels of a car each weigh 25kg and have a radius of 0,3m. Without its wheels, the car weighs 10^3 kg. The wheels are homogenous cylinders. What is the total kinetic energy of the car and the wheels if the car is moving at a speed of 30 m/s?
Homework Equations
[tex]K_{tot}=4(0.5I_{CM}\omega^{2}+0.5MV_{CM}^{2})+K_{car}[/tex]
the first to terms of the last question concern the wheels
[tex]I_{cylinder}=\frac{MR^{2}}{2}[/tex]
[tex]\omega=\frac{V_{CM}}{R}[/tex]
The Attempt at a Solution
replacing omega by V/R, I by MR^2/2 and distributing the 4:
[tex]K_{tot}=MV^{2}+2MV^{2}+\frac{10^{3}\times30}{2}[/tex]
[tex]K_{tot}=25\times30^{2}+50\times30^{2}+\frac{10^{3}\times30}{2}=82,2 \mathrm{kJ}[/tex]
The right answer is 518 kJ
where is the mistake? :(
thank you, sorry for my english