Download posttest ans - Aurora City Schools

Answer key__
Name: __
Pretest Score: _____/39
Postest Score: _
39_/39
Ch 10.3 & 11Forces: Pre-Test
Match each definition on the left with its correct term on the right.
R__ when an object is changing speed or
1. __
direction or both it is experiencing this
A. g
B. balanced force
and opposite reaction force
C. force
D. free fall
motion
E. friction
F. gravity
they move; can be rolling or sliding
G. inertia
H. kinetic friction
(amount) and direction of a force
I. Law of Universal Gravity
J. net force
center of an object, proportional
to mass
K. Newtons
L. Newton’s 1st Law of Motion
M. Newton’s 2nd Law of Motion
the force of gravity, can only happen
in outer space or a vacuum
N. Newton’s 3rd Law of Motion
O. resultant
P. static friction
N__ for every action force there is an equal and
2. __
B__ net (total) force = 0, no change in
3. __
H__ force of objects rubbing together when
4. __
S__ an arrow used to show the magnitude
5. __
F__ force that pulls things towards the
6. __
D__ when an object is moving only due to
7. __
A__ 10.0 m/s2
8. __
E__ force that opposes motion, air resistance
9. __
is an example
C__ an action on an object that changes its
Q. terminal velocity
R. unbalanced force
S. vector
T. weight
10. __
motion
T__ mass x acceleration due to gravity,
11. __
changes when you go to different
planets
G__ tendency of an object to not want to change motion
12. __
M__ F=ma; acceleration on an object depends on the net force acting on it and
13. __
I
its mass
14. __ __ Gm1m2/d2; the force of gravity between two objects depends on their
masses and the distance between them
Q__ when the acceleration due to gravity is balanced by air resistance; you
15. __
won’t go any faster as you fall
J__ the sum of all forces acting on an object
16. __
P__ force between surfaces that are not moving
17. __
K__ units that force is measured in; equals 1kg x 1m/s2
18. __
L__ an object at rest stays at rest and an object in motion stays in motion
19. __
unless acted upon by an unbalanced force
O__ in a drawing of forces, the sum of all the force acting on an object
20. __
21. How can you tell if the forces on an object are balanced? How will it be moving?
It will not be accelerating…that is, it will either
be at rest or have a constant velocity (both speed
and direction)
22. How can you tell if the forces on an object are unbalanced? How will it be
moving?
It will be accelerating; changing either its speed
or direction or both
23. You drop a golf ball and a bowling ball from the top of your house at the same
exact time. Which one will hit the ground first? Why?
They will hit at the same time (especially if
ignoring air resistance) because all objects fall
at the same rate…9.8m/s2.
The bowling ball has more mass, so
gravity pulls more, but also more inertia and
their effects “cancel” each other out.
24. You shoot a golf ball and bowling ball from a cannon. Which would accelerate
faster? Why?
Golf ball. Given the same force, it has a
smaller mass so a bigger acceleration
25. When you are in a car that turns to the right, why does your body lean to the
left? Which of Newton’s Laws of Motion applies here?
Newton’s First Law of Motion
You don’t lean to the left…you are an
object in motion and you stay in motion at the
same speed/direction until acted upon by an
unbalanced force…the seat belt, I hope….
26. If you drop a bowling ball from 100 feet high on the Moon and Earth, will it fall
faster on the Moon, on Earth, or at the same rate in either place? Why?
Earth…has more mass, therefore more
Gravity and things accelerate faster.
Matching: Which of Newton’s Laws of Motion is exemplified below? Put a 1 for 1st, 2
for 2nd and 3 for 3rd.
2__ When a traffic light turns green, a motorcycle goes faster than a truck
27. __
1__ If you pull a paper towel slowly, they all come undone. If you pull it
28. __
quickly only one does
2__ It takes more effort to push a car than to push a baby carriage
29. __
3__ When a bowling ball hits the pins, the pins change the direction of the
30. __
bowling ball
3__ A book sitting on a table is pushing down on the table, but the table is
31. __
holding the book up
400N___ A girl has a mass of 40 kg.
32. ___
What is her weight? Explain your
answer.
Weight = mass x g (acceleration due to
gravity 9.8 m/s2)
400N (I rounded to 10.0 m/s2 and weight
is a force, so its measured in N)
40 N_____ You push a grocery cart with a certain amount of force.
33. ____
The
grocery cart has a mass of 20 kg and when you push it, you
accelerate it at a rate of 2.0 m/s2. With what force did you
push the cart? Show your work below.
F=ma
F = 20 kg x 2.0 m/s2
F = 40 N
34. What forces are acting on the grocery cart in the previous problem? Draw a
diagram and label the forces that are acting and use arrows to show the
direction that they are acting. Are all of these forces the same strength or are
some stronger than others?
normal
friction
applied
g
Note: applied is greater than friction.
Since there’s acceleration forward, the
forces are unbalanced.
35. While being pushed in a rolling chair at a constant speed, you tilt your head up
and spit your gum out of your mouth, straight up in the air. If you continue to
move at this constant speed, could you catch the gum in your mouth again
without changing your position? Or will the gum land ahead of you? Or will
the gum land behind you?
Yes, you can. The gum is moving forward
at the same speed you are (object in motion)
and the up/down motion has no effect on the
forward motion.
36. What forces are acting on the person on the chair in the previous problem? Draw
a diagram and label the forces that are acting and use arrows to show the
direction that they are acting. Are all of these forces the same strength or are
some stronger than others?
normal
friction
applied
g
Note: friction and applied are the same.
Since there’s constant speed, (no acceleration)
the forces are balanced.
37. You punch a wall really, really hard. Is more force applied to the wall or to your
fist during the punch? Why is this?
Same to both. For every action force
there is an equal and opposite reaction
force. Your hand moves more because it
has less inertia (1st Law) or because with
the same force, it has less mass so
accelerates more (2nd Law)
38. What are the action and reaction force pair in the previous problem?
Action…you hit the wall
Reaction…the wall “hits” back.
Note: the force pairs happen:
 At the same time
 In the same magnitude (amount)
 In opposite directions
 On different objects (wall, you)
300 N of force and student B pushes the
refrigerator the opposite way with 100 N of force at the same time. Draw
39. Student A pushes a refrigerator with
and label arrows that are to scale that represent the forces from each student
and one that represents the result of the two forces combined.
My scale: 1 block = 25 N.
Result is 200N in direction of 300 N