The following Activities on string tension are for the Fletcher's Trolley applet. Make sure you know how the applet functions by consulting Help, Assumptions, and ShowMe under Applet Help on the applet's Help menu.

Activity 1. This Activity is for the case of negligible pulley mass.

Exercise 1. RESET the applet. The mass of Block 1 is not variable in the applet and equal to 600 g. Set the mass of Block 2 to 400 g and the mass of the pulley to 0.

The applet uses for the magnitude g of the acceleration due to gravity the value 9.8 m/s². Using this value, calculate the weight of Block 2, the block suspended from the pulley. Compare this weight to the tensions T₁ and T₂ in the ends of string attached to Blocks 1 and 2, respectively, when the system is held at rest. The values of the tensions are displayed in the Data box.

Exercise 2. Continuing from Exercise 1, display the free-body diagrams for the two blocks. Observe the lengths of the force vectors labeled T₁ and T₂. Then release Block 1 (by Playing the motion) and observe T₁ and T₂ during the motion. To make this easier, Pause the motion before Block 2 reaches the platform at the bottom. Are the tensions when the system is in motion different from when the system is held at rest? If so, are they larger or smaller when the system is in motion?

Do the ends of string attached to Blocks 1 and 2 still have equal tensions when the system is in motion, as they did when the system was held at rest?

Exercise 3. For the mass values in Exercises 1 and 2, calculate the tension in the string when the system is in motion, and compare your value to that displayed in the data box.

Exercise 4. Repeat Exercises 1 to 3 for a different value of the mass of Block 2.

Exercise 5. Derive an expression for the tension in the string in terms of the masses m₁ and m₂ of the blocks and the magnitude g of the acceleration due to gravity when the system is moving. The expression should involve symbols only, not numbers.

Activity 2. This Activity investigates qualitatively whether the the tensions in the ends of string attached to Blocks 1 and 2 are affected by the mass of the pulley.

Exercise 1. RESET the applet. Set the mass of Block 2 to 400 g and the mass of the pulley to 1.00 kg.

Compare the weight of Block 2 to the tensions T₁ and T₂ in the string on the sides of the pulley attached to Blocks 1 and 2, respectively, when the system is held at rest. The values of the tensions are displayed in the Data box.

Exercise 2. Continuing from Exercise 1, display the free-body diagrams for the two blocks. Observe the lengths of the force vectors labeled T₁ and T₂. The two tensions should be equal as long as the system is held at rest.

Release Block 1 (by Playing the motion), and observe T₁ and T₂ during the motion. To make this easier, Pause the motion before Block 2 reaches the platform at the bottom. Do the ends of string attached to Blocks 1 and 2 still have equal tensions when the system is in motion, as they did when the system was held at rest? If not, which tension is larger and how do the two tensions compare to the tension when the system is at rest?

Exercise 3. Repeat Exercises 1 and 2 for a different value of the pulley mass. Would you expect the new pulley mass to lead to tension values larger or smaller than those for the old pulley mass? Do your observations agree with your expectation?

Exercise 4. Attempt to explain your observations in Exercises 1 to 3 qualitatively.