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# Simple torque question?

I have copied two questions from my textbook, and am unsure how to compute these, could any community members help me ? 5 stars, best answer.

Motor torque required to accelerate 1000 kg family sedan from 0 to 100 km/h in 5.6 seconds

when riding on 380mm diameter wheelbarrow wheels. (Assume constant acceleration)

I'm a little confused regarding what the question is trying to ask, motor torque ?

Also another question,

Motor torque required to accelerate a samurai sword of mass 2.5 kg on the end of a 1.2m arm

to an impact velocity of 10 m/sec through a swing of 120 degrees. You may assume the

sword is a point mass at the end of the arm, giving a moment of inertia J=mr2

What would be the answer, and how would I calculate these two questions ?

Thank you,

Kind Regards,

Frank

.

### 2 Answers

- JimLv 77 years agoFavorite Answer
I'll try #2:

Torque = Jα

J = 1/2mR² = (0.5)(2.5)(1.2)² = 1.8 kg-m²

w{final} = final angular speed = V/R = 10/1.2 = 8.33 rad/s

w{avg} = 8.33/2 = 4.17 rad/s {assumes •constant• angular acceleration}

angular distance = 120° = 120/2π = 19.1 rad = Θ

Θ/w(avg) = time to accelerate = t = 19.1/4.17 = 4.58 s

α = w{final}/t = 8.33/4.58 = 1.82 rad/s²

Jα = 1.8(1.82) = 3.28 m-N ANS

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- 3 years ago
There ought to certainly be some thing incorrect with the numbers... appearing some 'opposite engineering', utilising the suggestion given and the respond from the e book, i stumble on that the fulcrum must be the two: * at 0.3 m with the ten kg mass on its left... which isn't conceivable or * at a million.8 m with the ten kg mass on its authentic... it somewhat is likewise no longer conceivable

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