# Torque Rquired for stages of motion

#### Bikerz

The fuel storage yard is seperated from the main plate by a swingbridge (swinging in a horizontal plane). The motor driving the briudge has to swing through an angle of 90degrees in 120seconds. The bridge accelerates uniformly for 40s then moves at a constant velocity, decelerating uniformly to rest in the final 20 s. The rotaing components of the bride have an equivalent moment of inertia of 400kgm² and feels a constand resisting torque of 3kN,. Find Torque of 3 stages of montion?

How do I go about this?
Which equations should I be using?

Torque = Inertia x Angular acceleration
Angular Velocity = Angle/dt (Time I presume)

I have done

sa=((V+0)/2)40=20V
sb=((V+V)/2)60=60V
sc=((0+V)/2)20=10V

I could then do

W=dØ/dt
Then times by Inertia (400)

I get

a-200N
b-400N
c=200N

This seems too easy and whast the resisting torque value for? Do I just add this to part a, ignor for part b and take off for part c?

Tho I'd get a negitive vale for c then?

Cheers

Sheldon

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#### nvn

Science Advisor
Homework Helper
You can use the fundamental kinematics equations to develop an expression for the total rotation angle of the swing bridge, then solve for alpha1, the angular acceleration during stage 1. Once you obtain alpha1 and alpha3, you can compute the applied torque of the three stages. Are you sure your mass moment of inertia and resisting torque given above are correct? After all, 3 kN is not a torque, so what you typed doesn't make sense yet. Try it again. Post a valid attempt to get help.

#### Bikerz

3kNm. Sorry.

Sent what I did to my lecture and he said it was right and he oppoligsed for teh strange number sin teh question that made me have answers that I thourght must be wrong.

All sorted

Cheers

Last edited:

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