Suggestions:
- Point C (the point on the bar that is in contact with the corner) must have its velocity aligned with the bar. The reasoning for this is that it cannot have a component of velcoity perpendicular to the bar; otherwise it would be lifting off the corner or penetrating the corner).
- Point A has a velocity to the left along the horizontal surface.
- The velocity of A must be the same as the velocity of point D on the pulley since the cord does not stretch.
- Write a rigid body velocity equation relating the velocities of points A and C: v_C = v_A + omega x r_C/A. Using the results from 1.-3. above in this velocity equation gives the relationship between the angular velocity of the drum (omega_0) and the angular velocity of the bar (omega). [Note that this vector velocity equation has two components (x and y) and gives us TWO scalar equations in terms of TWO unknowns: omega and the speed v_A.]
6 comments:
Sir
M having difficulties with 5/37.
I started with V_c=V_a + W X r_CA
so i got..V_c=(-W*h-r*W0)i+(-W*x)j
I cant see what other hints we have to go on from there. What do you suggest ?
Thanks
Your equation for V_c looks correct (you got this from the rigid body equation relating points A and C).
Now you need to use the known direction of V_c (see list item 1. in the post). Use this to write V_c in terms of x- and y-components from this constraint. Set this equal to your equation. Solve for omega of the bar.
I keep getting x^2-h^2 in the denominator, would that more than likely be a cross product error?
cawatson
hmm im having some difficulty find the direction of V_c, I have created a unit vector in terms of h and x and therefore have an i and j component, but the simplification isn't working well for me. Is this the right idea?
steve-o ..m kind of having the same problem..
item 1 tells us to put vector V_c in terms of i and j..but wouldnt it be in terms of [V_c] too, which is unknown?
Yes, it would be in terms of [V_c], but you are also finding two terms and have two unknowns. We you set up the problems in the i and j components that are all equal to each other, you can than get rid of this term by using it to set the two found equations equal to each other to make a new equation to solve for W.
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