1. You pull a box of mass 17 kg with a horizontal rope. The tension in the rope is 22 N. The box is pulled a distance of 3.2 m across a horizontal floor. (a) What was the work done on the box by the rope’s tension? (b) What was the work done on the box by the normal force? (c) What was the work done on the box by the weight force?
2. A spring of spring constant 220 N/m is sitting on a table. You pick it up and stretch it so that it is 8.0 cm longer than it was on the table top. How much work did it take you to stretch the spring? (Hint: This work is just negative the work done by the spring on you!)
3. You are slowly lowering a 15-kg box of tools from a roof top by means of a vertical rope. You are lowering the box such that its velocity is a constant. The box is lowered a distance of 3.5 m. (a) What is the acceleration of the box? (b) What is the tension in the rope? (c) What was the work done on the box by the rope’s tension? (d) What was the work done on the box by gravity? (e) What was the net work done on the box? (f) What was the change in the box’s gravitational potential energy?
II. Some Standards
4. A block of mass 5.0 kg sits on a rough horizontal surface of coefficient of friction 0.12. A force of magnitude F = 10.0 N pulls on the mass at an angle of 30o above the horizontal. The block is observed to move across the surface a distance of 2.3 m. (a) What is the work done by the force F? (b) What is the value of the apparent weight of the block? (c) What is the work done by the normal force? (d) What is the work done by friction? (e) What is the work done by the gravitational force acting on the block?
5. This problem refers to problem #8 in Lecture 10.(Click on the link to go to that problem statement. Then Click on the Back button on your browser to return to this page.) You will need the numbers in that problem to help you solve this one. During their game of tug-of-peace, the cooler is found to move a distance of 1.2 m at a slow but steady velocity towards Alfonso. The game is won by Alfonso after 57 s. (a) What was the work done by Bubba-Joe during the game? (b) What was Alfonso’s power output during the game?
6. You will need information from problem #11 in Lecture 10 to work this problem.(Click on the link to go to that problem statement. Then Click on the Back button on your browser to return to this page.) It takes Freddy 30 s to lower the box 2.0 m along the incline. (a) What was the work done by Freddy? (b) What was the average power supplied by the gravitational force? (c) What was the change in gravitational potential energy of the box?
III. So, you think you’re pretty good...?
7. A block of mass 15 kg is being pulled up an incline of angle 30o and coefficient of friction 0.12 by a rope. The tension in the rope is 120 N, and is directed parallel to the incline. The block moves a distance of 1.7 m in a time of 33 s.See problem #2 in Lecture 10. (Click on the link to go to that problem statement. Then Click on the Back button on your browser to return to this page.) (a) What is the value of the block’s apparent weight? (b) What is the magnitude of the block’s acceleration? (c) What is the work done on the block by the normal force? (d) What is the work done on the block by the block’s weight? (e) What is the work done on the block by the rope? (f) What is the power delivered to the block by the rope? (g) At what rate is energy being taken from the block by friction? (h) What was the change in gravitational potential energy of the block as it moved up the incline?
8. In problem #5 in Lecture 10(click on the link at left to go to that problem statement, then Click on the Back button on your browser to return to this page), what was the work done by (a) the normal force on Herbert? (b) The gravitational force? (c) What was the power supplied by the gravitational force in pulling Herbert to the bottom of the hill? (d) What was Herbert’s change in gravitational potential energy during his slide down the hill?
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