Physics CPA Midterm Review January 2014

Tags Physics, Motion, Velocity

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

Precision-

Degree 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 -

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!)?

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.

V = 0

a = constant

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

B. Vectors and Projectiles

12. Definitions and examples:

a) Vector-

b) Scalar-

c) 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

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

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

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

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 real-life examples.

Increase impact time air bag, packaging, catching with “give”

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

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

39. Work to Energy

a) When you lift a mass against gravity:

W = F x D

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

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?

4 x

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