The U.S. Department of Energy had plans for a 1500-kg automobile to be powered completely by the rotational kinetic energy of a flywheel. The 300-kg flywheel (included in the 1500-kg mass of the automobile) has a 6.0-kg⋅m2 rotational inertia and can turn at a maximum rotational speed of 3600 rad/s. Part B How many accelerations from a speed of zero to 15 m/s could the car make before the flywheel's energy was dissipated, assuming 100% energy transfer and no flywheel regeneration during braking?

Respuesta :

Answer:

230

Explanation:

[tex]\omega[/tex] = Rotational speed = 3600 rad/s

I = Moment of inertia = 6 kgm²

m = Mass of flywheel = 1500 kg

v = Velocity = 15 m/s

The kinetic energy of flywheel is given by

[tex]K=\dfrac{1}{2}I\omega^2\\\Rightarrow K=\dfrac{1}{2}6\times 3600^2\\\Rightarrow K=38880000\ J[/tex]

Energy used in one acceleration

[tex]K=\dfrac{1}{2}mv^2\\\Rightarrow K=\dfrac{1}{2}1500\times 15^2\\\Rightarrow K=168750\ J[/tex]

Number of accelerations would be given by

[tex]n=\dfrac{38880000}{168750}\\\Rightarrow n=230.4[/tex]

So the number of complete accelerations is 230

The rotational kinetic energy of a flywheel is 3.89 × 10⁷ Joules. The number of accelerations the car could make before the flywheel's energy is dissipated is 230.52

The rotational kinetic energy of a flywheel can be determined by using the formula:

[tex]\mathbf{K_i = \dfrac{1}{2} I \omega ^2}[/tex]

[tex]\mathbf{K_i = \dfrac{1}{2} (6.0 \ kg.m^2) \times (3600)^2}[/tex]

[tex]\mathbf{K_i = 3.89 \times 10^7 \ Joules}[/tex]

The kinetic energy of the system is:

[tex]\mathbf{K.E = \dfrac{1}{2}mv^2}[/tex]

[tex]\mathbf{K.E = \dfrac{1}{2}\times 1500 \times (15) ^2}[/tex]

K.E = 168750 Joules

The number of accelerations the car could make before the flywheel's energy is dissipated can be computed as:

[tex]\mathbf{n = \dfrac{3.89 \times 10^7 \ Joules }{168750 \ Joules}}[/tex]

n = 230.52

Learn more about rotational kinetic energy here:

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