Physics Mechanical Equilibrium Chapter 2 Solutions

Name ___________________________ Chapter 2 Class __________________ Date ____________ Mechanical Equilibrium Exercises 2.1 Force (pages 13–14) pull push 1. A force is a or a . motion 2. A force is needed to change the state of of an object. 3. Is the following sentence true or false? If an object is sliding on ice, it will true continue sliding until a force slows it down. 4. Define net force. the combination of all forces acting on an object Match the applied forces on an object with the letter of the corresponding net force on the object. Applied Forces d 5. 6. 7. 8. a b c 5 N to the right and 5 N to the left 4 N to the right and 6 N to the left 7 N to the right and 5 N to the left 6 N to the right and 4 N to the right Net Force a. b. c. d. 2 N to the left 2 N to the right 10 N to the right 0 N (no change in motion) 9. Describe the forces that act on a rock at rest in your hand. Your hand pushes upward on the rock with as much force as Earth’s gravity pulls down on it. 10. Circle the letter that identifies the force acting upward on an object suspended from a spring scale. a. gravity b. equilibrium c. tension d. weight vector 11. A is an arrow that represents the magnitude and direction of a quantity. 12. Explain the difference between a vector quantity and a scalar quantity. A vector quantity is a quantity that describes both magnitude and direction. A scalar quantity can be described by magnitude only and has no direction. 13. Write V beside each vector quantity. Write S beside each scalar quantity. S S a. time b. area S V c. force d. volume Name ___________________________ Chapter 2 Class __________________ Date ____________ Mechanical Equilibrium 2.2 Mechanical Equilibrium 14. Express the equilibrium rule in words. Whenever the net force on an object is zero, the object is said to be in mechanical equilibrium. 15. Express the equilibrium rule mathematically, and explain what the symbol in the rule means. ¤F = 0; the symbol ¤ means “the sum of.” 16. Circle the letter that describes the forces acting on a suspended object at rest. a. The forces acting upward on the object are greater than the forces acting downward on the object. b. The forces acting upward on the object are less than the forces acting downward on the object. c. The forces acting upward and downward on the object are balanced. d. No forces are acting on the object. 2.3 Support Force (page 17) 17. Identify the two forces acting on a book at rest on a table. State the direction of each force. a. The weight of the book due to gravity acts downward. b. The support force provided by the table acts upward on the book. support 18. The force is the upward force that balances the weight of an object on a surface. Another name for this force is the normal force. 19. Look at the drawing above. Explain how the force of the table pushing up on the book is similar to what happens when the spring is compressed. When the spring is compressed, it pushes upward on your hand. Similarly, the book sitting on the table compresses the atoms of the table. The atoms then push upward on the book. Name ___________________________ Chapter 2 Class __________________ Date ____________ Mechanical Equilibrium 20. Circle the letter that describes an object at rest on a horizontal surface. a. The support force is equal to the object’s weight. b. The support force is greater than the object’s weight. c. The support force is less than the object’s weight. 2.4 Equilibrium for Moving Objects (pages 18–19) constant 21. If an object is moving at a speed in a straight-line path, it is in a state of equilibrium. 22. Is the following sentence true or false? If a desk is pushed at a constant speed across a horizontal floor, the force of friction must be equal in magnitude and opposite in direction to the pushing True force on the desk. static 23. Objects at rest are said to be in equilibrium. 24. Objects moving at constant speed in a straight-line path are said to be in dynamic equilibrium. 2.5 Vectors (pages 19–22) 25. Suppose a gymnast with a weight of 300 N is suspended by a single 300 N vertical rope. What is the tension in the rope? 26. Now suppose the same gymnast hangs from two vertical ropes. What 150 N in each rope are the tensions in the ropes? the sum of two or more vectors 27. Define resultant. 28. State the parallelogram rule. To find the resultant of two vectors, construct a parallelogram wherein the two vectors are adjacent sides. The diagonal of the parallelogram shows the resultant. 29. The gymnast shown below is suspended from two non-vertical ropes. The solid vector represents the gymnast’s weight. What does the dashed vector represent? the resultant of the tensions in both ropes