We are once again using a simulation: PhET Forces and Motion. You will additionally need a stopwatch of any variety (phone/web stopwatches work fine). Part 1: Average Acceleration 1. Select the "Motion" tab of the simulation. 2. Check the boxes for "Values," "Masses," and "Speed." 3. Simultaneously press the"+50N" force button three times and start your stopwatch. 4. After approximately 5s press the "-50N" button three times and stop your stopwatch. o Question 1: What was your final time on the stopwatch? What was the final speed of the crate on the skateboard? Question 2: What is the average acceleration? Use the final and initial speeds as well as time to compute the average acceleration. o Question 3: Compute the expected acceleration via Newton's second law. Compare this to your answer from Q2. Reminder, an excellent way to compare two individual numbers is % difference. o Question 4: Which of Newton's laws do we observe after the force was set to zero in step 4? Explain. Part 2: Adding Friction 1. Select the "Friction" tab at the bottom of the sim. 2. Check the boxes next to "Values," "Masses," and "Speed" once again. 3. Simultaneously press the"+50N" force button three times and start your stopwatch. 4. Stop your stopwatch and press the "-50N" button another three times when the crate reaches the same speed as observed in Part 1. o Question 5: What were the speed and time when you stopped the stopwatch? o Question 6: Did this process take more or less time that was needed to achieve the same speed in part 1? What does that imply about the acceleration? Question 7: Compute the net acceleration and force. Use the definition of acceleration, and Newton's second lawo Question 8: Use the net force computed in Q7 and the applied force of 150N to compute the force due to friction. Additionally, find the coefficient of friction. . To find the coefficient of friction (# ) it will be helpful to know that Ffric = UN where N is the normal force (and in this case it is equal to weight). o Question 9: What happens to the box after we stopped pushing it? Explain (using Newton's laws). Part 3: The Mystery Box 1. Put the crate away, and replace it with the mystery box. 2. Follow the exact same process that we used in Part 2 to set up the summation of horizontal forces. 3. Use the definition of friction Ffric = MNV, along with the normal force (in this case: N = mg) to compute the mass of the mystery box. o Question 10: Assuming the coefficient of friction is the same as it was in part 2, compute the mass of the mystery box