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DISCUSSION and HINTS

Recall the following four-step plan outline in the lecture book and discussed in lecture:

Step 1: FBDs
Draw single free body diagram (FBD) for the entire system.

Step 2: Kinetics (Work/energy equation)
Consider all of the external forces that you included in your FBD above. Which forces, if any, do non-conservative work on that system? If there are no such forces, then energy is conserved. Write down the expressions for kinetic and potential energy for the initial and final states of the motion.

Step 3: Kinematics
At this step, you need to relate the speeds of blocks A and B at the second state. Consider using the instant center (IC) approach for the rigid link for position 2. Block B moves along a horizontal surface, and Block A rides on a vertical guide. Where do the perpendiculars to these two velocity vectors intersect? Take a look at the freeze-frame of the animation of the motion at state 2 shown below. Does that image agree with your IC analysis? And, what does this say about the speed of block B at that state?

Step 4: Solve
Combine your kinetics equation from Step 2 with your kinematics that you found in Step 3, and solve for the speed of A.

Discussion and hints:

Recall the following four-step plan outline in the lecture book and discussed in lecture:

Step 1: FBD
Draw a free body diagram of the system made up of P. Which, if any, forces do non-conservative work on this system? Can you justify this from the FBD?

Step 2: Kinetics (work/energy equation)
Write down the work energy equation for P. Recall that the potential energy in a spring is 0.5*k*Δ², where Δ is the stretch/compression in the spring. Δ is NOT equal to the length of the spring. Recall that the spring is unstretched at position 2.

Step 3: Kinematics
What kinematics do you need here?

Step 4: Solve
Solve your work/energy equation for the speed of P at position 2.

Any questions??