Problem statementSolution video |

**DISCUSSION THREAD**

Any questions??

**Discussion**

Suppose that you decide to use the following velocity and acceleration equations:

**v**_{A} = **v**_{O} + (**v**_{A/O})_{rel} + **ω** x **r**_{A/O
}** a**_{A} = **a**_{O} + (**a**_{A/O})_{rel} + **α** x **r**_{A/O} + 2**ω** x (**v**_{A/O})_{rel} + **ω** x (**ω** x **r**_{A/O})

using an observer that is attached to link OB. With this choice, the angular velocity and acceleration of the observer are those of link OB:

* ω* =

**ω**_{OB}

**k**

α = αα = α

_{OB}**k**

Now to the question of what motion does the observer see for point A. The observer see A moving back and forth along the x-axis, where the x-axis is attached to OB:

*( v_{A/O})_{rel }= b_dot i*

*(*

**a**_{A/O})_{rel }= b_ddot**i**Note that A is traveling on a circular path of radius R at a constant speed *v _{A}*. What does this say about the velocity and acceleration vectors for A and B,

*and*

**v**_{A }*at this instant? Watch the animation above to confirm your response.*

**a**_{A},

Using the suggestions, finding the angular acceleration/ velocity of OB, is this still the same for the angular acceleration/velocity of the arm?

Aekum: Yes, the arm and OB have the same rotation rate. Why are you asking about the arm rotation rate?

Since the problem states that end A of the arm is moving with a constant speed v_A, does that make the acceleration of the arm at A equal to zero? Because the animation shows an acceleration vector at A throughout the entirety of its motion, even at the instant shown in the problem. Or since the entire arm is moving about the slot with radius R there is the acceleration at end A in the positive x direction and it would just be the acceleration in the y direction that equals zero?

Ethan: Think back to the second day of class when you were studying the path description for kinematics. On that day, you learned that the acceleration of a point moving on a curved path has two distinct components: one tangent to the path (rate of change of speed) and one normal to the path (centripetal component). The problem states that A is moving with a constant speed; therefore, the rate of change of speed of A is zero, and A has ONLY a centripetal component of acceleration. The component that you see in the animation is always perpendicular to the path, and is the centripetal component: (v^2/rho)*e_n.

Have the solutions not been posted yet?

When I try to view them is says "Sorry you cannot view this page"