Download Conceptual Physics

Physics CPA
2014
Midterm Review
January
A.1-D Motion and Measurement
1. Vocabulary and formulas:
Distance- how far
Displacement – final position – initial position
Speed- total distance /time
Velocity- average velocity – change in position/time, instantaneous
velocity = speed ion a certain direction
Acceleration- rate of change of velocity, result of a non-zero net force
PrecisionDegree of fineness, repeatability of results
Accuracy- closeness of measurement to true value
2. Experimental design:
The Experiment: how does launch velocity affect range of the
projectile?
Independent Variable –
Dependent Variable –
Controlled Variables –
Hypothesis –
Procedure –
Data to be collected -
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How does data measurement affect the number of digits
recorded and used in calculations? (significant digits)
Problems
3. Calculate the distance traveled by a walker who travels at a
constant speed of 5.0 km/hour after 2.5 hours. (12.5 km)
4. Calculate the acceleration of a car that can go from rest to 30
m/s in 5 seconds. (6m/ss)
5. Calculate the speed of a car after 5 seconds if it has been
accelerating at 2.0 m/s2. (10 m/s)
6. What is the speed of an object at rest? If an object travels at a
constant speed, what is its acceleration?
7. Objects in free fall:
8. In order to accelerate, an object must have:
Net external force
D. Free Fall
7. What is the acceleration due to gravity (include the units!)?
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8. What is the acceleration of an object in free fall? (ignoring air
resistance)
9. What is the impact speed of an object that is dropped from a height
and hits the ground after 2 seconds? (20 m/s)
a) After 4 s? (40 m/s)
10. An object is thrown straight upwards with initial speed V0.
a) Draw a sketch of the object’s path, labeling its velocity at the
top and bottom.
b) Label the object’s acceleration at the top and bottom of its
path.
c)
V=0
a = constant
vmax
vmax
11. If the terminal velocity of a falling object is 25 m/s, about how fast
is it falling after:
1 s?
10 m/s
2 s?
20 m/s
3 s?
25 m/s
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B. Vectors and Projectiles
12. Definitions and examples:
a) Vectorb) Scalarc) Projectile-
13.
Definitions and sketch a not-to-scale vector diagram:
a) Headwind-
b) Tailwind-
c) Crosswind-
14. Calculate the resultant velocity of an airplane that normally flies
at 250 km/h if it encounters a headwind of 50 km/h. (200 km/hr)
a) What if it encounters a tailwind of 50 km/hr? (300 km/hr)
15. If a massive rock and a tiny pebble are simultaneously dropped
from a bridge, neglecting air resistance, which would strike the
ground first?
same
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16. If two projectiles are released at the same time, but one is
dropped, while one is projected horizontally, which will hit the
ground first?
Why?
Same, only height and gravity matter
17. What factors affect the horizontal range of a horizontally
launched projectile? (lab)
Launch velocity and launch height
18. What is the projectile’s acceleration in the horizontal direction?
In the vertical direction?
19.What is the ideal angle of projection for maximum horizontal
range?
45 degrees
C. Forces and Newton’s Laws
20. Definitions and formulas
a) Mass- amount of matter, measure of inertia
b) Inertia- resistance to acceleration, mass
c) Force- push or pull
d) Newton’s first law- If net force = 0 then body is at rest or at
constant velocity. If net force is NOT zero, then body will
accelerate.
e) Weight- gravitational force
f) Equilibrium- net force = 0
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g) Pressure- force/area
h) Newton’s Second law F net = ma
i) Newton’s Third Law
Forces come in action reaction pairs
18. List 4 different forces along with a brief description
a) Gravity - Weight
b) Tension – rope or string
c) Normal - surface
d) Friction- resists sliding between surfaces
19. What is the formula you use to find an object’s weight?
Weight = mg
20. If a man has a mass of 70 kg, how much does he weigh? (on
earth) (700 N)
21. If a cart is being moved by a certain net force, and that force is
then halved, what effect would the change in force have on the
cart’s acceleration?
½ F, 1/ a
F = ma
22. A force acts upon a mass, resulting in an acceleration. How
can you double the acceleration? How can you triple the
acceleration?
To double a, double F, to triple a, triple F
F= ma
F= ma
To double a, ½ m, to triple a, 1/3 m
23. What is the net force acting on an 5 kg object when it is being
pushed at constant velocity across the table? The applied force is
15 N.
a) Sketch a free-body diagram
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b) What is the magnitude of the frictional force? (15 N)
c) Suppose the applied force is increased to 20 N. Determine
- The new net force (5 N)
- The acceleration of the object (1 m/s2)
24. What is the net force acting on a 50 N object that is in free-fall,
ignoring air resistance?
Sketch a free-body diagram. Net force = 50 N
25. Pressure = force/area
26. Standing on one foot cause the pressure exerted on the floor to
double because area was cut in half.
Using snowshoes cause the pressure exerted to decrease
because area is increased.
27. Examples of action-reaction force pairs:
a) Ball on bat: bat on ball
b) Foot on ground: ground on foot
c) Hammer on nail:nail on hammer
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d)
28. Three properties of action-reaction force pairs:
a) They are equal in magnitude
b) They are opposite in direction
c) They act on opposing objects
D. Impulse and Momentum
29.
Definitions and formulas
a) Impulse- F-t
b) Momentum- p = mv
30. How can an object be given a maximum change in
momentum? Use the impulse momentum formula
Give two real-life examples.
Increase Force and impact time
Braking, hitting a baseball
31. How can the impulse equation help you deliver a large force to
an object? Use the impulse momentum formula. Give at least
one real-life example.
Small impact time, large impact velocity
Boxer, breaking an egg
32. How can the impulse equation help you reduce the force on
an object? Use the impulse momentum formula. Give two reallife examples.
Increase impact time air bag, packaging, catching with “give”
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33. According to conservation of momentum, if the momentum of
the system before the collision is equal to ‘X’, the momentum after
the collision is equal to X
No external forces acting
34. A loaded fright car has 5 times as much mass as an empty
freight car. If the loaded car coasts at 5 m/s and collides with and
attaches to the empty car at rest, what is the speed of both cars
together after the collision?
vf = 4.2 m/s
35. A 30-kg girl and a 50-kg boy are at rest on friction-free roller
skates. The girl pushes the boy, who moves away at 3 m/s.
What is the girl’s speed?
V = 5 m/s in the opposite direction
36. A 70-kg astronaut on a space walk fires 0.10 kg of gas at a
speed of 30 m/s from his propulsion gun. What is his recoil speed?
V = .0428 m/s in the opposite direction
E. Work and Energy
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37. Definitions/Formulas
a) Work- transfer of energy by mechanical means: F-d
b) Potential Energy-stored energy mgh
c) Kinetic energy- energy of motion ½ mv2
d) Power = W/t
38.
Work and Power
a) How much work does friction do in applying 5 N of force to a
block and stopping it in 0.3 meters?
1.5 J
b) How much work is done when a 60-kg person runs up a 4.0
m flight of stairs?
2400 J
c) How much Power is generated by the person if he completes
the stair run in 1.5 s?
1600 W
d) If a 75 kg person also raced up the stairs in the same time,
would he generate more, less or the same Power? Why?
More: more mass = more Work = more Power
e) Which light bulb converts more energy per hour of use a 100
W incandescent bulb or a 20 W compact fluorescent bulb?
100 J/s
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39. Work to Energy
a) When you lift a mass against gravity:
W=FxD
b) How much Work is required to lift a 5.0 kg block to a height
of 2.0 m?
100 J
c) What is the Potential Energy of the block at the 2.0 m height?
100 J
40.
Energy in Motion
a) Formula-
41. A 2000-kg truck travels at 5 m/s. A 1000-kg car travels at 10
m/s. How do their kinetic energies compare?
Bigger truck so 2x the energy
But ½ the velocity so ¼ the energy
So truck has ½ the KE of the car
42. What does this say about the braking force needed to stop a
car as its speed increases?
43. If two vehicles are moving at the same speed, but one has
three times the mass of the other, the work needed to stop the
heavier vehicle will be:
3 x that of the smaller vehicle.
Why???
Work = change in Kinetic energy
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44. If two cars have the same mass, but one is moving at twice
the speed. All other things being equal, it has a stopping distance
that is
how many times the slower car?
4x
Why??
45. Calculate the Potential energy of a 1.0 kg apple in a tree branch
2.0 m high.
20 J
46. What is the total energy of the apple as it falls to the ground?
20 J
47. How much kinetic energy does the apple have when it is at a
height of 1.0 m
PE = 10 J, KE = 10 J
48. If the apple has less kinetic energy than expected upon impact,
what is the most likely reason?
Energy lost as heat
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