Kinematics of Rigid Bodies question

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Discussion Overview

The discussion revolves around a kinematics problem involving a uniform pole hinged to a truck bed, which is released from a vertical position as the truck accelerates. Participants explore the relationships between linear and angular motion, considering the effects of constant acceleration on the pole's angular velocity as it reaches a horizontal position.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant notes the relevance of several equations but expresses uncertainty due to the lack of mass for the pole, questioning how this affects the calculations.
  • Another participant confirms that the last formula provided by the first poster is valid for constant angular acceleration, suggesting that the acceleration remains constant from vertical to horizontal position.
  • A different participant highlights the dual accelerations acting on the pole: one due to the truck's acceleration (0.9 m/s² to the left) and the other due to gravity (9.8 m/s² downward), indicating confusion about which acceleration to use in the calculations.
  • Another reply suggests taking moments about the hinge point and incorporating pseudo forces, proposing a formula for angular velocity that includes both gravitational and truck acceleration effects, leading to an approximate angular velocity of around 3.

Areas of Agreement / Disagreement

Participants express differing views on how to approach the problem, particularly regarding which accelerations to consider and how to apply the relevant equations. There is no consensus on the correct method or final answer.

Contextual Notes

Participants note the absence of mass for the pole, which may affect the application of certain equations. The discussion also reflects uncertainty regarding the integration of forces and the assumptions made about constant acceleration.

Who May Find This Useful

This discussion may be useful for students and educators interested in kinematics, particularly in understanding the dynamics of rigid bodies under acceleration and the application of angular motion equations in complex scenarios.

DTskkaii
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Homework Statement


The uniform 3.6m pole is hinged to the truck bed and released from the vertical position as the truck starts from rest with than acceleration of 0.9m/s^2. If the acceleration remains constant during the motion of the pole, calculate the angular velocity of the pole as it reaches the horizontal position.
Diagram attached.

Homework Equations


I believe these equations are relevant, however, I am not given a mass for the pole, so I'm not entirely sure.
a(tangential)=mrθ''
a(normal) = mrω^2
ƩMo=Iθ''+Ʃma(vector)d
I=k^2m
ω=2Vx
ω=(ωo^2+2aθ)^(1/2)

The Attempt at a Solution


So I eventually want to realize the angular velocity ω.
I have done a similar question that utilised energy and momentum methods, however, with a negligible mass, I'm not sure whether that will affect the equations, since the example question used mass.

So essentially, I believe it may be using the last formula I provided, since it is not determined by time or mass.
So, all I need to find is the acceleration, since I already know that ωo is at rest, and θ=90. Finding the acceleration, from the given positive direction of acceleration of the truck body, is something that I can't figure out.

Thankyou for any feedback!
 

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your last formula is valid for constant angular acceleration,so from vertical to horizontal position does it remain the same.
 
@ Andrien
Well, the pole accelerates to the left (opposite the direction of the car) at 0.9m/s^2, and accelerates downward at 9.8m/s^2.
These are both constants, but I don't know which to use in the formula.
It can't possibly as simple as angular vel=(0^2+2*0.9*90)^1/2
 
consider taking moment about hinge point, and write ma as a pseudo force along with gravity which will act towards left i.e. opposite to acceleration of truck.integrate from 0 to pi/2,you will get
w=[3(g+a)/l]^.5, where l= length of rod.assuming k^2=l^2/12,
w is around 3.
 

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