3. Negative work on a block. A block is moving to the right in outer space while touching only an astronaut's hand. A hand exerts a constant force on the block. The work done on the block by the hand is negative. The hand's force is either to the left or to the right (but you are not told which directly). Draw arrows below to show the direction of the displacement of the block and the direction of the force by the hand. Displacement of the block Force on block by hand a. Explain how you chose the direction of the force on the block by the hand. W b. Does the total energy of the block increase, decrease, or stay constant? Explain. (Assume the block does not change potential energy.) Hint: Is the block speeding up, slowing down, or moving with constant speed? nisloxa 4. Consider the definition of work. How do you determine if work is positive, negative, or zero? 5. You are told that in a problem, the work done on an object is -5J. Can you say anything about the direction of the object's displacement? 6. If the direction of force and displacement are known, does the sign of work change if the positive direction is reversed (e.g. positive was previously to the left and is now to the right)? Explain. Checkpoint. Please continue working. elegy sold ent no anob how ien ent el fox3 Plooki edi no scio 474. Based on your answer above, how does the energy of a system change when the net work done on the system is positive, negative, or zero? net work done on the system is AE system positive negative zero 5. Is this idea consistent with the conservation of energy? Note: we will not cover potential energy until next week, so we tell you that here the system of the box above does not change potential energy. Checkpoint. Please continue working. Tutorial Section 4.4 - Work, and the directions of force and displacement 1. Complete section 1C from the Work and Work-Energy Theorem in the tutorial book (pg. 40). 2. A student pushes a refrigerator until she breaks a sweat. The fridge does not move. Does the student do any work on the fridge?' Answer using: a. your intuition. b. the physics definition of work. 3. In this scenario, does the student a. give the fridge any kinetic or potential energy? 1 Based on the approach in http://www.physics. umd.edu/perg/OSTutorials/07_Work_and_Energy/Tutorial_07_W_and_E.dochow b. expend energy, i.e., use some chemical energy stored in her body? If so, where does this energy go? Consider the description of the conservation of energy in the explanation packet. 4. The student says, "I'm definitely doing work pushing on this fridge. I'm exhausted!" How can you explain this student's experience alongside the physics definition of work? Using your knowledge of the definition of work, explain why gravity does not do work on an object that slides horizontally across the ground. Checkpoint. Please continue working. Tutorial Section 4.5 - The definition of work, and conservation of energy (part 2) Glider A is pulled by a string across a level, frictionless table. The string exerts a constant horizontal force Complete Section IIA and IIB of the Work and the Work-Energy Theorem in the tutorial book. Checkpoint. Please continue working. How to noninijeb adleyly or Tutorial Section 4.6 - Revisiting the experiment Consider the first experiment from section 1. 1. How much work does each force do on the glider during your first experiment? Consider forces in both the horizontal and vertical directions. Why? 2. What is the net work done on the glider in your first experiment? 50