Newton’s Laws Concept Questions

1. Newton’s Laws Concept Questions Clicker Questions/WS Key

2. 1. It is possible to have motion in the absence of a force. • True • False 34 4

3. 2. What is the tension in the cable of an elevator with a weight of 8800 N that ascends with an acceleration of 1.30 m/s2? • Draw the free body diagram • Sum the forces in the y direction • Solve for tension • 9967 N ~ 1.0 x 104N

4. 3. If an object isn’t moving, no external force acts on it. • True • False 2 36

5. 4. If a single force acts on an object, the object accelerates. • True • False 28 9

6. 5. A 500. N stoplight just turned red. • What is the mass of the stoplight? 51.0 kg • What is the weight of the stoplight? 500. N • What is the force of gravity on the stoplight? 500. N

7. 6. If an object isn’t accelerating, no external force is acting on it. • True • False 6 32

8. 7a. A small sports car collides head on with a massive truck. Which vehicle will experience the greatest magnitude force? • The car. • The truck. • Neither, it is the same

9. 7b. A small sports car collides head on with a massive truck. Which will undergo the greater magnitude acceleration? • The car. • The truck. • Neither, it is the same.

10. 8. If the net force acting on an object is in the positive x-direction, the object moves only in the positive x-direction. • True • False 16 20

11. 9. Calculate the acceleration of the system & the tension in the rope. 2.67 m/s2 towards the 175 kg mass 175. kg 100. kg

12. 10a. When throwing a baseball, a force is exerted by the hand on the ball. Is this force a field force or a contact force? • Field Force • Contact Force

13. 10b. Throwing a ball 6 m straight upwards requires a 25 N throwing force. How strong is the throwing force it experiences when the ball is half way to the top? • More than 25 N • Less than 25 N (but more than 0 N) • Exactly 25 N • 0 N 1 12 12 10

14. 11. If an object is accelerating, a force is acting on it. • True • False 33 4

15. 12. A full moving box has a mass of 20.0 kg. If a net force of 30. N is applied to it, what is its acceleration? 1.5 m/s2

16. 13. A space explorer is moving through space far from any planet or star. He notices a large rock, taken as a specimen from an alien planet, floating around the cabin. Should he push is gently or kick it toward the storage compartment? Why? • Push it gently so he doesn’t fly off away from it. • Kick it. 28 5

17. 14. Identify the action reaction pairs in the following situations: • Snowball hits a girl in the back. • A baseball player catches a ball. • A man takes a step. • A gust of wind strikes a window.

18. 15. A truck loaded with sand accelerates along a highway. If the driving force stays the same on the truck, what happens to the truck’s acceleration if its trailer leaks sand at a constant rate through a hole in the bottom? • Acceleration increases. • Acceleration decreases. • Acceleration stays the same. 34 1 3

19. 16. Calculate the magnitude (number, not direction) of the resultant vector: X Y 20. N 40. N 25o 15 N

20. 17. A passenger sitting in the rear of a bus claims that she was injured as the driver slammed on the breaks, causing a suitcase to come flying towards her from the front of the bus. If you were a judge in this case, how would you rule and why? • Judge should rule in the lady’s favor because she is telling the truth. • Judge should rule against the lady because she is lying. 5 31

21. 18. Tiger Woods can hit a golf ball with 55 N of force. How hard does the ball hit back on the club? • More than 55 N of force • Less than 55 N of force • Exactly 55 N of force 1 8 27

22. 19. B, A, F, C, D, E • Two forces act on an object on a frictionless surface. • Rank each situation from greatest to least change in velocity (note all vectors directed to the right are positive, and those to the left are negative. Also 0 m/s > -10 m/s

23. 20. What action reaction pair is responsible for pushing a car forward? • Tires push on the ground, ground pushes back on tires.

24. 21. A rubber ball is dropped to the floor. What force causes the ball to bounce? Does the Earth “bounce” too? 6 • Ground pushing back on the ball; Yes • No 27

25. 22. While rummaging in her backpack for her cell phone, Sally’s Mini-Cooper rear ends Joey’s Suburban. Sally’s car is totaled while the suburban is fine. If Sally’s car hit the suburban with 30 N of force, how much force did Joey’s car exert on Sally’s? • More than 30 N of force • Less than 30 N of force • Exactly 30 N of force 1 1 34

26. 23. Helpful Henry’s car is pushing Flat-tire Fred’s car to the car shop. While the cars are accelerating up to 15 miles/hour Helpful Henry needs to push Fred’s car with 60 N of force. With what force does Flat-tire Fred’s car push on Helpful Henry’s car? • More than 60 N of force • Less than 60 N of force • Exactly 60 N of force 1 3 32

27. 24. An army plane wants to drop supplies to a group of physics students stranded on an island. In order for the package to land on the island, the pilot needs to drop the package before the plane is directly above the island. Explain why using Newton’s Laws (you may ignore air resistance). • Newton’s 1st law explains this. • Newton’s 2nd law explains this. • Newton’s 3rd law explains this. 31 5 2

28. 25. • A 55 kg person is standing on a 10.0o hill. Calculate the coefficient of friction between the person’s shoes and the hill so that the person stays standing in place instead of sliding down the hill. • .18 • Is this the coefficient of static friction or of kinetic friction?