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Newton's Laws of Motion Problems by fjwuxn

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Newton’s Laws of Motion

DIRECTIONS: On a separate sheet of paper, answer each of the questions as fully as possible
to receive full credit. You may use your notes.

1. Why does a child in a wagon seem to fall backward when you give the wagon a sharp pull?

2. When a golf ball is dropped to the pavement, it bounces back up. (a) Is a force needed to
make it bounce back up? (b) If so, what exerts the force?

3. Explain, using Newtons first and second laws, the motion of your leg during one stride while
walking.

4. A person wearing a cast on an arm or leg experiences extra fatigue. Explain this using of
Newtons first and second laws.

5. If the acceleration of a body is zero, are no forces acting on it?

6. Why do you push harder on the pedals of a bicycle when first starting out than when moving
at constant speed?

7. Only one force acts on an object. Can the object have zero acceleration? Zero velocity?

8. When you are running and want to stop quickly, you must decelerate quickly. What is the
origin of the force that causes you to stop?

9. Why might your foot hurt if you kick a heavy desk or a wall?

10. When you stand still on the ground, how large of a force does the ground apply to you? Why
doesn’t this force make you rise into the air?

11. A ball is held in a person’s hand. (a) Identify all the external forces acting on the ball and the
reaction force to each. (b) If the ball is dropped, what force is exerted on the ball while it is
falling? Identify the reaction force in this case. (Neglect air resistance)

12. If a car is traveling westward with a constant speed of 20 m/s, what is the resultant (net) force
acting on it?

13. If a car moves with constant acceleration, can you conclude that there are no forces acting on
it?

14. If gold were sold by weight, would you rather buy it in Denver or Death Valley? If it were
sold by mass, in which of the two locations would you prefer to buy it? Why?
15. A passenger sitting in the rear of a bus claims that she was injured as the driver slammed on
the brakes, causing the suitcase to come flying toward her from the front of the bus. If you were
the judge in this case, what decision would you make (agree or disagree)? Why?

16. A space explorer is moving through space far from any star or planet. She notices a large
rock, taken as a specimen from an alien planet, floating around the cabin of the ship. Should she
push it gently or kick it toward the storage compartment? Why?
17. What set of action/reaction forces cause an automobile to move? A propeller-driven
airplane? A rowboat?

18. Analyze the motion of a rock dropped in water in terms of its speed and acceleration as it
falls. Assume that a resistive force (friction) is acting on the rock as the velocity increases.

19. In the motion picture It Happened One Night, Clark Gable is standing inside a stationary bus
in front of Claudette Colbert, who is seated. The bus suddenly starts moving forward and Clark
falls into Claudette’s lap. Why did this happen?

20. Describe a few examples in which the force of friction exerted on the object is in the
direction of motion of the object.

21. A large crate is placed on the bed of a truck, but not tied down. (a) As the truck accelerates
forward, the crate remains at rest relative to the truck. What force causes the crate to accelerate
forward? (b) If the driver slams on the brakes, what could happen to the crate? Explain.

22. A truck loaded with sand accelerates along the highway. If the driving force remains
constant, what happens to the truck’s acceleration if its trailer leaks sand at a constant rate
through a hole in its bottom? Why?

23. Identify the action-reaction pairs in the following situations: (a) a man takes a step, (b) A
snowball hits a girl in the back, (c) a baseball player catches a ball, (d) a gust of wind strikes a
window.

24. The driver of a speeding empty truck slams on the brakes and skids to a stop through a
distance d. (a) If the truck carries a load that doubles its mass, what would happen to the truck’s
skidding distance? (b) If the truck’s initial speed were cut in half, what would happen to its
skidding distance? Explain each in terms of Newton’s first and second laws.

25. If the Earth’s mass were double what it is, in what ways would the Moon’s orbit be different?

26. The Sun is directly below us at midnight, in line with the Earth’s center. Are we then heavier
at midnight, due to the Sun’s gravitational force on us than we are at noon? Explain.

27. People sometimes ask, “What keeps a satellite up in its orbit around the Earth?” How would
you respond?

28. A father and his seven year old daughter are facing each other on ice skates. With their
hands, they push off against each other. (a) Identify the action-reaction forces. (b) Compare the
force of each push. (c) Which one, if either, experiences the larger acceleration? Explain in
terms of Newton’s second law.

29. When a body is moved from sea level to the top of a mountain, what changes – the body’s
mass, weight, or both. Explain your answer.

30. Why do you lunge forward when your car suddenly comes to a stop? Why are you thrown
backward when your car rapidly accelerates? In your explanation, refer to the most appropriate
one of Newton’s three laws of motion.

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