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Newton's First Two Laws

1. Which is more fundamental, mass or weight? Does an object with mass have weight? Does an object with weight have mass?

2. Could an object have mass without having weight? Could an object have weight without having mass?

3. Why does a 2 kg brick have twice the inertia of a 1 kg brick?

4. In the orbiting space shuttle you are handed two identical boxes, one filled with sand the other filled with feathers. How can you tell which is which without opening the boxes?

5. Why is a massive cleaver more effective for chopping vegetables than an equally sharp and less massive knife?

6. In tearing a paper towel or plastic bag from a roll, why is a sharp jerk more effective than a slow pull?

7. Since the earth rotates once every 24 hours, the western wall in the classroom moves in a direction towards you at a linear speed that is about 1000 km/h. When you stand facing the wall you are carried along at the same speed, so you don't notice it. But when you jump upward, with your feet no longer in contact with the floor, why doesn't the wall slam into you at about 1000km/h?

8. Can an object round a curve without any force acting upon it? Explain

9. To pull a wagon across a lawn with a constant velocity, you have to exert a steady force. Reconcile this fact with Newton's first two laws, which state that motion at constant velocity requires no net force.

10. As you were leaping into the air during the hang time lab, how did the force that you exerted on the ground compare with your weight? Explain

11. You find an object that is not moving and you know it is being acted on by a force, how do you explain this to your confused friend?

12. When a car moves along the road at a constant velocity, the net force is zero. Why does the engine have to keep running?

13. What is the net force on an apple that weighs 1 N as you hold it at rest above your head? What is the net force on it after you release it?

14. A cart is pulled to the left with a force of 100 N, and to the right with a force of 30 N. What is the net force on the cart?

15. If the net force on a sliding block is tripled, by how much does the acceleration increase?

16. If the mass of a sliding box is tripled while a constant force is applied, by how much does the acceleration decrease?

17. If the mass of a moving object is tripled just as the net force on it is tripled, how is the acceleration effected?

Newton's Second Law Problems

18. Find the acceleration of a 2.000 x 103 kg, single engine airplane just before takeoff when the force of the engine is 500.0 N.

19. What is the acceleration of a 3.00000 x 106 kg jumbo jet just before takeoff if each of its four engines produces 3.0000 x 105 N of force.

20. Calculate the acceleration if you push with a 20.0 N horizontal force on a

2.00 kg block of wood on a friction-free air table.

21. What would the acceleration of the wood block in #3 be if there was a frictional force of 4.0 N.

22. Calculate the horizontal force that must be applied to produce an acceleration of 9.8 m/s2 for a 1.0 kg puck experiencing no friction.

23. What is the mass of an object that is accelerated at a rate of 1.8g by a net force of 21.2 N?

Newton's Third Law

24. Consider hitting a baseball with a bat. If the force of the bat pushing on the ball is the action force, what is the reaction force?

25. When do action and reaction pairs of forces not cancel/balance one another?

26. If the forces that act on a bullet and the recoiling gun from which the bullet is fired are equal in size, why do the bullet and gun have very different speeds?

27. How does a helicopter get its lifting force?

28. As you sit in a chair, does the chair exert an upward force against your derriere (french for behind) How much force does it exert? Why doesn't the chair fly up into the air when you stand up?

29. Consider the forces acting on you as you sit in your seat, the downward pull of gravity and the upward support of your seat. Are these forces equal and opposite? How do you know? Do they form an action - reaction pair? Explain.

30. For each of the following forces, what is the equal and opposite force required by Newton's third law? (a) The force of a hammer on a nail. (b) the force of gravity pulling down on a book? (c) the force of a helicopter blade pushing down on the air. (d) the force of air resistance acting on a falling baseball.

31. You hold an apple over your head. (a) Identify all the forces acting on the apple and their reaction forces. (b) When you drop the apple, identify all the forces acting on it as it falls and the corresponding reaction forces.

32. If a Mack truck and a Honda Civic have a head-on collision, upon which vehicle is the impact force greater? Which vehicle experiences the greater acceleration? Explain each answer.

33. Which team wins in a tug-of-war; the team that pulls harder on the rope , or the team that pushes harder on the ground? Explain.

34. A horse pulls a heavy wagon with a certain force. The wagon, in turn, pulls back with an opposite but equal force on the horse. Doesn't this mean the forces cancel one another, making acceleration impossible? Why or why not?

35. Suppose two carts, one twice as massive as the other, fly apart when the compressed spring that joins them is released. How fast does the more massive cart roll compared to the other less massive cart? Explain.

Non-freefall

36. What is the net force on a 10 N falling object that encounters 4 N of air resistance? 10 N of air resistance?

37. What two principal factors effect the force of air resistance on a falling object?

38. What is the acceleration of a falling object that has reached its terminal velocity?

39. Why does a heavy parachutist fall faster than a lighter one who wears the same size parachute? This is referring to after the parachute is opened.

40. Is a skydiver who has reached terminal speed in freefall? Explain

41. How does the weight of a falling body compare with the air resistance it encounters before it reaches terminal velocity? After?

42. Why is it that a cat that falls from the top of a 50 story building will hit the ground at the same speed as it would if it fell from the 20th story?

43. If and when Galileo dropped two balls from the top of the Leaning Tower of Pisa, air resistance was not really negligible. Assuming the balls were the same size and shape, one made of wood and the other of metal, which ball struck the ground first? Explain

44. What is the acceleration of a rock at the top of its flight when thrown straight upward? Explain

45. What will be the acceleration of a skydiver when air resistance builds up to be half her weight?

Momentum problems

46.What is the momentum of a 0.50 kg hockey puck traveling at 50.0 m/s?

47. A 1.5 kg football is thrown with a momentum of 22.5 kg . m/s. What is the velocity of the football?

48. The momentum of a train traveling at 50 m/s is equal to the momentum of a 1.0000 x 104 kg plane that is traveling at 2500 m/s. What is the mass of the train? If the two collide head-on what will be the velocity of the resulting pile of metal?

49. The momentum of a 0.2 kg bullet is 100 kg . mi/h. How fast is the bullet traveling?

50. What would be the momentum of a 1500 kg truck moving at 20 m/s? Would this momentum be different on the moon? Explain and give new momentum if necessary.

Conservation of momentum and Impulse

51. Which has a greater momentum, a heavy truck at rest or a moving skateboard?

52. What are the two ways to increase impulse?

53. For the same force, which cannon gives the larger speed to a cannonball - a long cannon or a short one? Explain.

54. Why might a glass survive a fall onto a carpeted floor but not onto a concrete floor?

55. Why would it be a bad idea to have the back of your hand up against the outfield wall when you catch a long fly ball?

56. Which undergoes the greatest change in momentum: (a) a baseball that is caught, (b) a baseball that is thrown, or (c) a baseball that is caught and then thrown back, if the baseballs have the same speed just before being caught and just after being thrown?

57. When a bullet is fired, its momentum changes! And the momentum of the recoiling rifle changes. So momentum is not conserved for the bullet, and momentum is not conserved for the rifle. Why can we say that when a rifle fires a bullet, momentum is conserved? Why does the bullet by itself not violate the law of conservation of momentum?

58. Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A?

59. If the same two cars in the previous question stick together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A.

60. Two automobiles, each of mass 1000 kg, are moving at the same speed, 20 m/s, when they have an inelastic collision. In what direction and at what speed does the wreckage move if one car was driving north and the other south?

61. Can you run fast enough to have the same momentum as an automobile rolling at 1 mi/h? Justify your answer.

62. A railroad diesel engine is four times as massive than a freightcar. If the diesel engine coasts at 5 km/h into a freightcar that is initially at rest, how fast do the two coast after they couple together?

63. Itís not the fall that hurts you, itís the sudden stop! Use the language of math to verify this statement with a real example.

64. Explain why it is a good thing that you did not bounce in the previous question.