May asked in Science & MathematicsPhysics · 2 years ago

# How many accelerations from a speed of zero to 12 m/s could the car make before the flywheel's energy was dissipated?

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.

I found the maximum rotational kinetic energy which is:

3.9x10^7 J

I'm just unsure how to approach the question asked above.

Relevance
• NCS
Lv 7
2 years ago

The KE acquired by the car at 12 m/s is

KE = ½ * 1500kg * (12m/s)² = 1.08e5 J

So, how many times does this value go into 3.9e7 J?

Hope this helps!

• 2 years ago

your energy stored, KE(rotational)= (1/2)* i *w^2

=0.5 * 6* 3600^2

= 3.8 *10^7 j

• oubaas
Lv 7
2 years ago

Stored energy in the flywheel Ekf :

Ekf = J/2*ω^2 = 6/2*3.6^2*10^6 = 3.8880*10^7 joule

stored energy in the car each acceleration Ekc :

Ekc = m/2*V^2 = 0.75*10^3*1.2^2*10^2 = 1.080*10^5

n = Ekf/Ekc = 360.0 times