Accelerating a car including the moment of inertia of the wheels

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The discussion revolves around calculating the acceleration of a car considering the moment of inertia of its wheels. The car accelerates from rest with a given engine torque, and participants explore the relationships between torque, frictional force, and angular acceleration. Key equations include τ = Iα and a = αR, with emphasis on drawing free body diagrams for each wheel to clarify forces. Participants also discuss using energy concepts to simplify calculations, ultimately arriving at the correct expression for acceleration as a = 2τ / R(M + 6m). The conversation highlights the importance of correctly accounting for the mass of the wheels and their rotational inertia in the overall dynamics of the car.
  • #31
lichenguy said:
I started with:
2τΔθ = 1/2Mv2 + 4*1/2mv2 + 4*1/2Iω2
then
v2 = 2τΔθ/(1/2)M+3m

Next i have to multiply the denominator by 2(xf-xi)=2RΔθ, that's what gives me the factor of 6. Did you get the factor of 3 earlier?

Can the OP or someone else explain how that equation was simplified to get a factor of 3 in the denominator for "m"?
The original equation involves a term with rotational kinetic energy (1/2Iω2).

Was that "I" for the object's inertia converted to some kind of equivalent mass?
 
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  • #32
NewtonianAlch said:
Can the OP or someone else explain how that equation was simplified to get a factor of 3 in the denominator for "m"?
The original equation involves a term with rotational kinetic energy (1/2Iω2).

Was that "I" for the object's inertia converted to some kind of equivalent mass?
Each wheel is treated as a uniform, solid cylinder for which I = (1/2)mR2. Also, for rolling without slipping, ω = v/R.
 
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  • #33
TSny said:
Each wheel is treated as a uniform, solid cylinder for which I = (1/2)mR2. Also, for rolling without slipping, ω = v/R.

Thank you.

I was using I = mR2, hence why it didn't come out the same.
 
  • #34
NewtonianAlch said:
Thank you.

I was using I = mR2, hence why it didn't come out the same.
OK. Glad it makes sense now.
 

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