Problem statementSolution video |

**DISCUSSION THREAD**

**Discussion and hints:**

Recall the following *f**our-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*Δ^{2}, 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??

Since we consider potential energy of a spring a scalar and conservative force, we don't need to calculate the work it does on the way from position 1 to 2, right? Even though at the start the spring force has a y component opposing the gravitational force and is effectively reducing the weight?

Nope, the work we calculate is only if its a non-conservative force.