Download Unit 4 Force and Newton`s Law Review Key

KEY
Physics
Chapter 4 Vectors and Forces Part I Review
2015
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 A sheet of paper can be withdrawn from under a container of milk without toppling it if the paper is jerked away quickly.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
8.
d. 1000 kg
e. none of the above
Consider a person getting onto a bed:
a. How does the magnitude of the weight of the person on the bed compare to the added upward
support force the floor now puts on the bed? Equal
b. Do the person’s weight and the added support force from the floor comprise an action-reaction
pair? Why or why not? No. person/bed and person/earth are two different pairs.
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. Friction _____.
a. acts in a direction that opposes the motion of an object
b. comes from microscopic bumps that act as obstructions to the objects motion
c. is the name given to the force acting between surfaces sliding past one another
d. all of the above
e. none of the above
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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 the largest mass of gold if your chunk of gold weighed 1 N on _____.
a. the moon
b. Earth
c. it doesn’t matter which planet you are on.
13.
Which are true at equilibrium?
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 maximum resultant possible when adding a 3 N force and an 8 N force?
a. 24 N b.11 N c. 8 N d. 5 N e. 3 N
15. What is the minimum resultant possible when adding a 3 N force and an 8 N force?
a. 24 N b. 11 N c. 8 N d. 5 N e. 3 N
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. forces
d. masses
e. none of the above
18.
With a constant force, how does the acceleration of an object change in relation to its mass? It is
_____.
a. directly proportional
b. inversely proportional
c. acceleration doesn’t depend on mass at all
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
e. none of the above
21. A 10 kg brick and a 1 kg book are dropped in a vacuum. The force of gravity on the 10 kg brick is _____.
a. the same as the force on the 1 kg book
b. 10 times as much as the force on the 1 kg book
c. zero
21a. As in 21. The acceleration of the 10 kg brick is
a. the same as the acceleration of the 1 kg book
b. 10 times as large as the acceleration of the 1 kg book
c. zero
22. An apple weighs 1 N. The net force on the apple when it is in free fall is _____.
a. 0 N b. 0.1 N c. 1 N d. 9.8 N e. none of the above
23. 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
24. A girls 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
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25. 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
26. A force of 1N accelerates a mass of 1 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
27. A rock is thrown vertically into the air. At the top of its trajectory, the net force on it is _____.
a. less than its weight
b. more than its weight
c. equal to its weight
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
30. A student hits a nail with a hammer. During the collision, there is a force _____.
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. 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.
33. 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
34. 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
35. An unfortunate bug splatters against the windshield of a moving car.
a. the car
b. the bug
c. both the same
Which undergoes the greater change in velocity?
36. A person weighs 500 N. What is the mass of the person?
W = mg so m = 500N/10m/s2
m = 50kg
37. What is the resultant of a 5.0 N force acting vertically upward and a 3 N force acting to the right? Draw a FBD, then
be sure you add vectors properly.
32 + 52 = R2
tan -1( 3/5)
R = 5.8 N
59o CCW from +x
38. 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.
F = Wt = 200kg(9.8 m/s2) = 1960N
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39. 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?
F = (5kg)(2m/s2) = 10N
10N = 3kg (a)
a = 1/3 m/s2
40. 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?
A = F/m = 1N/2kg = 0.50 m/s2
x = 0 + ½ (0.5 m/s2) (2.0s)2 = 1.0 m
42. Two students are struggling over Mr. Wells’ favorite Physics book. One pulls horizontally with a force of 400 N
at 40° and the other pulls horizontally with 800 N at 290°.
a. Calculate the net horizontal force on the book. (Magnitude and direction)
Visualize the book pulled around on a table top. Don’t confuse the horizontal force with the X-direction force.
X-direction force is just one component of the horizontal force.
F = 763 N at 320°
b. What 3rd force (called the equilibrant force) would Mr. Wells have to supply to keep his book stationary
horizontally? (Magnitude and direction)
Opposite in magnitude and direction. 763 N at 140°
43. Bronco the skydiver, whose mass is 50 kg, experiences 100 N of air resistance. What is the acceleration of his fall?
Draw a FBD.
F = (50)(-9.8) + 100 = -390N (down)
a = F/m = -390N/50kg = -7.8 m/s2 (down)
A 40 kg block is pulled along the floor with a constant applied force of 85 N that acts at an angle of 55˚
above the horizontal. The force of friction 10 N.
44.
Fnet x = 48.8 – 10 N – 38.8 N
a = Fnet x / m = 1.2 m/s2
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45. A person with a blackbelt in karate has a fist that has a mass of 0.70 kg. Starting from rest, this fist attains a
velocity of 8.0 m/s in 0.15 s. What is the magnitude of the net force applied to the fist to achieve this level of
performance?
a = (8.0 m/s – 0)/ 0.15s = 53 m/s2
F = ma = 0.70kg(53m/s2) = 37N
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