Dynamics Homework Help - Verify Va & Aa Answers

[glitchy]

Hey all,

anyone help me verify the answer for the question

i got

Va=-5(root 3)i + 3j ft/s and
Aa=45i-29j ft/s^2

 

[RadiationX]

Why not host your image somewhere until it gets approval?

 

[eok20]

for the velocity, i got the j component to be 5. this would give it a speed of 10 which is equal to the speed of the other end which seems reasonable to me due to the symmetry of the problem when the rod is horizontal.

 

[glitchy]

eok20: you mind showin me you workin. I'm assumin you got the same for the 'i' component though?

 

[eok20]

yea, i got the same thing as you for the i component. what i did was find an expression involving the distance of end a (call it s_a) to the vertex and the distance of end b to the vertex (s_b). since the distance between a and b is always 2 and the ends stay on those lines, we know that (s_a*cos30 + s_b*cos30)^2 + (s_a*sin30-s_b*sin30)^2 = 2^2. then i differentiated with respect to time and put in 10 for ds_b/dt and 1/cos30 for s_a and s_b.

 

[glitchy]

i understood everything u said clearly apart from " then i differentiated with respect to time and put in 10 for ds_b/dt "

 

[eok20]

i differentiated both sides of the equation (s_a*cos30 + s_b*cos30)^2 + (s_a*sin30-s_b*sin30)^2 = 2^2 with respect to time, keeping in mind that s_a and s_b are both functions of time.

 

[glitchy]

i'm sorry, ur losing me a bit here. how can u differentiate with respect to time if you don't have a 't' in the whole thing. it's basically a constact.

 

[eok20]

the distance between each end and the vertex is changing over time-- ds_a/dt and ds_b/dt are both nonzero (in general).