What is the maximum attainable speed for the car?

  • #1

Homework Statement


P62 Sterling. #11
A new design for a car is to have a large disc like flywheel within the car storing kinetic energy. The flywheel has a mass of 370 kg witha radius of 0.5 meters and can rotate up to 200 revolutions a second. Assuming all of this store kinetic energy can be transferred to the linear velocity of the 1500 kg car what is the maximum attainable speed of the car?

Homework Equations


KE=(mv^2)*1/2

The Attempt at a Solution


I calculated the circumference of the wheel to be 3.14 m. If there are 200 revolutions per second then the wheel travels 628 m/s ( velocity of the wheel) . Using KE=(mv^2)*1/2, the kinetic energy is 7.3*(10^7)joules for the wheel.
Is the amount of energy that should be transferred to the 1500 kg car. 7.3*(10^7)joules = 1500(v^2 )*1/2. But the answer for velocity (4.7 *10^5)m/s I get is incorrect. It seems like this should work but it does not it seems like this should work but it does not. Why not?
 
Last edited:

Answers and Replies

  • #2
166
45
Your circumference calc is off by 10.
 
  • #3
Your circumference calc is off by 10.
Im sorry. The correct circumference in the problem is 0.5 m. So circumference calculation is correct. But the answer isn't off by a degree of 10 anyway :-(
 
  • #4
122
35
The energy stored in a flywheel is I ω*2 / 2 and the moment of inertia of a disk is m R^2 / 2 and of course the kinetic energy of the car moving down the highway is M v^2 / 2.
 
  • #5
The energy stored in a flywheel is I ω*2 / 2 and the moment of inertia of a disk is m R^2 / 2 and of course the kinetic energy of the car moving down the highway is M v^2 / 2.
Thank you. Liner kinetic energy needs to be calculated completely differently than rotational kinetic energy. Lol.
 

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