Physics - Allen Independent School District



Physics Unit 3 Review Name:__________________________

Use GUESS method on problems. Date:_________ Period:____________

1. Newton’s First Law states that an object _____.

a. at rest will remain at rest unless acted on by an outside force

b. will continue moving at the same velocity unless acted on by an outside force

c. will continue moving in a straight line unless acted on by an outside force

d. that is not moving will never move unless a force acts on it

e. all of the above

2. The law of inertia applies to _____.

a. moving objects b. objects at rest c. both moving and nonmoving objects

3. After a cannon ball is fired into frictionless space, the amount of forced needed to keep it going equals _____.

a. twice the force with which it was fired

b. the same amount of force with which it was fired

c. on half the force with which it was fired

d. one quarter the force with which it was fired

e. zero, since no force is necessary to keep it moving

4. A sheet of paper can be withdrawn from under a container of milk without toppling it if the paper is jerked away quickly. The reason this can be done is that _____.

a. the milk carton has very little weight

b. there is an action-reaction pair operating

c. gravity pulls very hard on the milk carton

d. the milk carton has inertia

e. none of the above

5. One object has twice as much mass as another object. The first object also has twice as much _____.

a. inertia b. velocity c. gravitational acceleration d. energy e. all of the above

6. Compared to its weight on earth, a 50 kg object on the moon will weigh _____.

a. less b. more c. the same amount

7. The mass of a dog that weighs 100 N is about _____.

a. 1 kg b. 10 kg c. 100 kg d. 1000 kg e. none of the above

8. The mass of a dog weighing 490N is ____.

a. zero b. 490 kg c. 20 kg d. 50 kg e. none of the above

9. An object following a straight line path at constant speed _____.

a. has a net force acting on it in the direction of motion

b. has zero acceleration

c. must be moving in a vacuum

d. has no forces acting on it

e. none of the above

10. Force is to Newtons as weight is to _________________.

a. kg b. m/s2 c. N d. kg m/s

11. A 10 N force west and a 30 N force east act on an object concurrently. What is the net force acting on the object?

a. 40 N east b. 30 N west c. 20 N east d. 20 N west e. none of the above

12. You would have a larger mass of gold if your chunk of gold weighed 1 N on _____. (THINK!!)

a. the moon b. Earth c. it doesn’t matter which planet you are on.

13. Equilibrium occurs when _____.

a. all the forces acting on an object are balanced

b. the sum of the forces acting rightward equal the sum of the forces acting leftward.

c. the sum of the forces acting upward equal the sum of the forces acting downward.

d. the net force is zero.

e. all of the above.

14. What is the resultant for a person that walks 9.0 m north then 12.0 m west?

a. 3.0 m NW b. 15.0 m NW c. 21. m NW d. 31 m NW

15. What is the direction the person has walked if he walked 9.0 m north then 12.0 m west?

a. northeast b. northwest c. southeast d. southwest

16. Which has more mass, a kilogram of feathers or a kilogram of iron?

a. the feathers b. the iron c. same masses

17. Accelerations are produced by _____.

a. velocities b. accelerations c. unbalanced forces d. masses e. none of the above

18. According to Newton’s second law, the acceleration of an object ______ its mass.

a. is directly proportional to

b. is inversely proportional to

c. doesn’t depend on

19. The acceleration produced by a net force on an object is _____.

a. directly proportional the magnitude of the net force.

b. in the same direction as the net force

c. inversely proportional to the mass of the object

d. all of the above

20. What is not one of the four fundamental forces?

a. gravity b. electric c. fire d. strong nuclear

21. If an object weighs 49 N on Earth, how much does it weigh on Mars if the gravitational acceleration on Mars is approximately 3.71 m/s2?

a. 5.0 N b. 13.2 N c. 18.6 N d. 49.0 N

22. An apple weighs 1 N. When held at rest on top of your head, the net force on the apple is _____.

a. 0 N b. 0.1 N c. 1 N d. 9.8 N e. none of the above

23. A girl pulls a 10 kg wagon with a net force of 30 N. What is the wagon’s acceleration?

a. 0.3 m/s2 b. 3.0 m/s2 c. 10 m/s2 d. 30 m/s2 e. 300 m/s2

24. An object has a constant mass. A constant force on the object produces constant _____.

a. velocity b. acceleration c. both A and B d. none of the above

25. A force of 100 N accelerates a mass of 100 kg at the rate of 1 m/s2. The acceleration of a mass of 2 kg acted upon by a force of 2 N is _____.

a. half as much b. twice as much c. the same d. none of the above

26. Which of the following forces is the weakest?

a. force of gravity b. electromagnetic forces c. weak nuclear force d. strong nuclear force.

27. Weight is equal to____________

a. mass (kg) b. 9.81 c. force due to gravity d. lbs on a scale

28. A block is dragged without acceleration in a straight line path across a level surface by a force of 6 N. What is the frictional force between the block and the surface?

a. less than 6 N b. more than 6 N c. 6 N d. need more information to answer

29. A tennis ball and a solid steel ball are sitting on a table. Which ball has the greatest net force acting on it?

a. the tennis ball b. the steel ball c. neither they are the same

30. A student hits a nail with a hammer. During the collision, there are forces _____.

a. on the hammer but not the nail

b. on the nail but not the hammer

c. on the nail and the hammer

31. Action/reaction forces always occur _____.

a. by themselves b. in pairs on the same object

c. in pairs on different objects d. in triplets

32. Complete the following Units Table

|Physical Quantity |Symbol |SI Unit |

|Time |t |s |

|Acceleration |a |m/s2 |

|Speed |v |m/s |

|Velocity |v |m/s |

|Displacement |Δd |m |

|Distance |d |m |

|Mass |m |kg |

|Force |F |N |

|Weight |Fg |N |

|Torque |ζ |N ∙ m |

33. If the torque required to loosen a nut on a wheel of a car has a magnitude of 40.0 N∙m, what is the minimal force must be exerted by a mechanic at the end of a .30 m wrench to loosen the nut?

|Givens: Torque ζ = 40.0 N∙m |Substitute: F = (40.0 N ∙ m) / .30 m |

|Distance d = 0.30 m | |

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|Unknown: Force F = ???? N | |

|Equation: ζ = F(d) F = ζ / d | |

| | |Solve: F = 133.3 N |

34. To tighten a bolt, you push with a force of 80 N at the end of a wrench handle that is 0.25 m from the axis of the bolt What torque are you exerting?

|Givens: Torque F = 80 N |Substitute: ζ = (80 N)(0.25 m) |

|Distance d = 0.25 m | |

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|Unknown: Torque ζ = ???? N∙m | |

|Equation: ζ = F(d) | |

| | |Solve: ζ = 20 N∙m |

35. Which of the following would produce the most torque?

a. a 10.0 N force applied at a perpendicular distance of 1.0 m

b. a 10.0 N force applied at a perpendicular distance of 2.0 m

c. a 10.0 N force applied at a perpendicular distance of 4.0 m

d. a 10.0 N force applied at a perpendicular distance of 8.0 m

36. Draw a FBD for the following scenarios. Be sure to describe the differences in acceleration, net force, equilibrium, and balanced forces

|Scenario A: A cake is sliding at constant velocity on a frictionless surface. |Scenario B: A cake is sliding to a stop. |

|FBD: |FBD: |

|Circle one: Moving or not moving |Circle one: Moving or not moving |

|Circle one: Accelerating or not accelerating |Circle one: Accelerating or not accelerating |

|Circle one: Nonzero net force or no net force |Circle one: Nonzero net force or no net force |

|Circle one: Equilibrium or not equilibrium |Circle one: Equilibrium or not equilibrium |

|Circle one: Balanced forces or unbalanced forces |Circle one: Balanced forces or unbalanced forces |

37. A 15 N object is pushed along a frictionless surface with a 20 N force to the right and a 20 N force to the left. The resulting net force in the x-direction causes

A) a balanced force

B) constant velocity

C) an unbalance force to the right

D) both A and B

E) none of the above

38. An archer shoots an arrow. Consider the action force to be the bow string against the arrow. The reaction to this force is the ____.

a. weight of the arrow.

b. air resistance against the bow.

c. friction of the ground against the archer’s feet.

d. grip of the archer’s hand on the bow.

e. arrow’s push against the bowstring.

39. An unfortunate bug splatters against the windshield of a moving car. Compared to the acceleration of the car, the acceleration of the bug is _____.

a. larger b. smaller c. the same

40. An unfortunate bug splatters against the windshield of a moving car. Compared to the force of the car on the bug, the force of the bug on the car is _____.

a. larger b. smaller c. the same

41. An unfortunate bug splatters against the windshield of a moving car. Which undergoes the greater change in velocity?

a. the car b. the bug c. both the same

42. A block is being pushed to the right with a force of 10 N along a flat table.

a. What direction and magnitude of force must be applied to produce a net force of zero? ________10 N left___________

b. What direction and magnitude of force must be applied to produce balance forces? ___________10 N left____

c. What direction and magnitude of force must be applied to have an unbalanced force that slows down the block? ___12 N left______

d. What direction and magnitude of force must be applied to have an unbalanced force that speeds up the block? ____8 N left______

Use the following diagram to answer the next six questions.

43. Is the following object experiencing balanced or unbalanced forces? _______unbalanced forces______________

44. Is the following object accelerating, moving at constant speed, or not moving at all? _______accelerating__________

45. What is the net force of this object in the x-direction? _____________70 N left______________

46. What is the net acceleration of this object in the x-direction? ________1.75 m/s2_________________

47. What is the weight of this object? _______392 N__________________

48. If the net force in the y-direction is balanced, what would the normal force of this object be? _____392 N______________

49. A person weighs 500 N. What is the mass of the person?

|FBD: (Given and Unknowns) |Equation: Fg = ma m = Fg / a |

| |Substitute m = (500 N) / (9.8 m/s2) |

| | |Solve: m = 51.0 kg |

50. What is the resultant of a person running with an average velocity of 5.0 km/hr south and then running with an average velocity of 3.0 km/hr west? Draw a diagram and then be sure you add vectors properly.

|Diagram: (Given + [pic] |Equation: a2 + b2 = c2 |

| |Substitute: (5)2 + (3)2 = c2 |

| |36 = c2 |

| |5.8 km/hr = c |

| | |Solve: c =5.8 km/hr |

51. A 200 kg bear grasping a vertical tree slides down at a constant velocity. What is the friction force between the tree and the bear? Draw a FBD.

|Diagram (Givens + Unknowns) |Equation: Fg = ma |

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| |Substitute: Fg = (200 kg) (9.8 m/s2) |

| |Fg = 1960 N |

| |Ff = Fg (since there is no net force since the bear is moving with |

| |constant velocity) |

| | |Solve: Ff = 1960 N |

52. A certain unbalanced force gives a 5 kg object an acceleration of 2.0 m/s2. What acceleration would the same force give a 30 kg object?

|FBD (Givens and Unknowns) |Equation: F =ma and F= ma |

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| |Substitute: F = (5 kg)(2 m/s2) = 10 N |

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| |F = ma 10 N = (30kg)(a) |

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| |Solve a = 0.33 m/s2 |

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53. A net force of 1.0 N acts on a 2.0 kg object, initially at rest, for 2.0 seconds. What is the distance the object moves during that amount of time? (Use GUESS method and think kinematics.)

|FBD (Givens and Unknowns) |Equation: F = ma Δd = vi(t) + (½)at2 |

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|F = 1.0 N m = 2.0 kg | |

|vi = 0 m/s | |

|t = 2 s | |

|Δd = ??? m | |

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| |Substitute: a = F /m a = (1.0 N) / (2.0 kg) = .50 m/s2 |

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| |Δd = vi(t) + (½)at2 Δd = (0 m/s)(2 s) + (1/2)(.50 m/s2)(2 s)2 |

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| |Solve Δ d = 1.0 m |

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54. Suppose you exert 400 N horizontally on a 50 kg crate on a factory floor. The friction between the crate and the floor is 200 N. What is the acceleration of the crate? Draw a FBD.

|FBD (Givens and Unknowns) |Equation: Fx = Fa – Ff and Fx = ma |

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| |Substitute: Fx = 400 N – 200 N = 200 N |

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| |Fx = ma a = Fx / m |

| |a = 200 N / 50 kg |

| |Solve a = 4.0 m/s2 to the right |

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55. A 50 kg block of cement is pulled upward, against gravity, with a force of 800 N. Draw a FBD. What is the acceleration of the block?

|FBD (Givens and Unknowns) |Equation: Fg = ma Fy = Fn – Fg Fx= ma |

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|Find anet | |

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| |Substitute: Fg = (50 kg)(9.8 m/s2) = 490 N |

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| |Fy = 800 N – 490 N = 310 N |

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| |Fx= ma a = Fx / m = 310 N / 50kg = 6.2 m/s2 |

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| |Solve a = 6.2 m/s2 |

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56. A 40.0 kg block is pushed along the floor with a constant applied force of 85.0 N. The block moves with constant velocity. Draw a FBD. Do the x forces balance? Do the y forces balance? What is the force due to friction? Calculate the normal force.

|FBD (Givens and Unknowns) |Eq Fg = ma Fn = Fg Fa = Ff |

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| |Substitute: Fg = (40 kg)(9.8 m/s2) = 392 N |

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| |Fn = 392 N Ff = 85.0 N |

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| |Solve: x forces balance and y forces balance since the is no |

| |net force because the block is moving with constant velocity. |

| |Fn = 392 N Ff = 85.0 N |

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57. Find the net force in the x-direction for the following scenario. Use the GUESS method and be sure to properly bubble your answer.

Given: Fg = 147 N a = 9.8 m/s2 downward

a= 8.0 m/s2 to the right

Unknown: Find m in ?? kg first, then fx in ??? N

Equations: Fg = ma then Fx = ma

Substitute: m = Fg / a = 147 N / 9.8 m/s2 = 15 kg

Fx = ma = (15 kg)(8.0 m/s2) = 120 N

Solve: Fx = 120 N

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Fg

Fn

Ff

Fg

Fn

Fa

??? N

10.0 N

65 N

85 N

40kg

90 N

Fn

ag = 9.8 m/s2

Fg = 500 N

m = ??? kg

5.0 km/hr

??? km/hr

3.0 km/hr

Ff = ?? N

m = 200 kg

ag = 9.8 m/s2

Fg = ?? N N

a = 2.0 m/s2

F = ?? N

m= 5 kg

F = ??? N

m = 30 kg

a = ??? m/s2

Fa = 400 N

Ff = 200 N

m = 50 kg

Find anet = ?? m/s2

Fn = 800 N

m =50 kg

ag = 9.8 m/s2

Fg = ?? N

Fx = 0 N

Fy = 0 N

Fn = ?? N

Ff = ?? N

Fa = 85.0 N

m = 40.0 kg

ag = 9.8 m/s2

Fg = ?? N

Fn = 147 N

a= 8.0 m/s2 to the right

Fg = 147 N

ag = 9.8 m/s2

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