H Physics 1st
Study Guide for Semester 1 Exam 2014
***Study your notes, labs, and assignments. You may also check out a book if you would like. Show equation used, all work and include units for full credit.
Formula Sheets You are expected to know all formulas, units, and variables covered during first semester.
You may use your own formula sheet in your own handwriting. Only formulas, units or variables may be on the sheet. No notes, vocabulary/definitions or examples of any kind. To be collected with TEST.
Distance, Displacement, Velocity and Acceleration
1. Describe the difference between scalar and vector quantities.
A vector is “something” with magnitude and direction. Ex. You drive 35 mph North on Cicero. 35 mph is the magnitude, North is the direction. Together they are a vector.
Scalar - only magnitude (size or number), no direction. Example - “I traveled 35 mph.”
2. Define and give an example of magnitude.
Magnitude is the size or the number. Ex. You drive 35 mph North on Cicero. 35 mph is the magnitude
3. Know how to add vectors graphically. Consider forces of 10N and 20N.
a. a 10N to the east and a 20N to the east
10N east + 20N east = 30N east
b. a 10N to the east and a 20N to the west
10N east + 20N west = 10N west
c. a 10N to the east and a 20N to the north
Use Pythagorean 10 2 + 20 2 = c2 100 + 400 = c2 500=c2 22.36 = c
4. A car travels 50 km to the north, 30 km to the west, 20 km to the south, 13 km to the west, and 30 km to the south.
What is the total distance traveled? ___143km____ Draw diagram:
What is the displacement of the car? ___43km west____
5. If a car travels at a constant speed of 25 m/s, how far does it travel in 30 seconds?
s = d/t 25 m/s = d/ 30s d = 750 meters
Going the same speed as #3b, how long does it take to travel 800m?
s = d/t 25 m/s = 800m/ s s = 32 seconds
6. A bicyclist is riding at a speed of 4 m/s, then accelerates at a rate of 1 m/s2 for 6 seconds. How fast is the cyclist going after 6 seconds?
a = ∆v = vf – vi 1 m/s2 = vf – 4 m/s 10 m/s
t t 6s
7. A car is stopped at a red light at the corner of 159th and Cicero. The car then accelerates to 35.0 mi/hr (15.6 m/s) in 8.0 s. What is the acceleration of the car?
a = ∆v = vf – vi a = 35m/s -0 m/s 4.37 m/s2
t t 8s
Gravity and Acceleration due to gravity
8. What is the value for acceleration due to gravity on earth? ______9.8 m/s2 or 10 m/s2______
9. If a bowling ball and tennis ball are released at the same (disregard any air resistance), which will hit the ground first? Explain. If you disregard air resistance than both should fall at the same rate hitting the ground at the same time.
10. Draw a diagram of a ball being thrown up in the air. Describe/label the diagram with the velocity and acceleration at the start, mid, and end point.
The acceleration is due to gravity and will always be a -9.8m/s2 indicating it is in the opposite direction of travel. The velocity at the beginning and end are equal with opposite signs. The velocity in the middle is zero.
Energy
11. Draw a diagram of a ball being thrown up in the air. Describe/label the diagram with the potential and kinetic energies at the start, mid and end point.
12. Roller coaster problem (assume no friction) start with v of 0m/s. Fill in the chart below (show work and include units.
13. Calculate the increase in potential energy when a 20 kg block of ice is lifted a vertical distance of 2 m.
PE = mgh PE = (20)(9.8)(2) = 392 J
14. A boulder is raised above the ground so its potential energy relative to the ground is 75 J. If the boulder falls, what is its kinetic energy just before it hits the ground?
75J (Maximum PE is equal to the Maximum KE right before it hits the ground)
15. A basketball player who weighs 600N jumps 0.5m vertically off the floor. What is her kinetic energy just before hitting the floor?
PE = (600N) (0.5m) = 300J so KE = 300J
Same as #14 (Maximum PE is equal to the Maximum KE right before it hits the ground)
Force, Weight, Mass
16. What is Newton’s first law? An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force.
a. What is inertia and on what property does inertia depend?
Inertia: the tendency of an object to resist changes in its state of motion
b. Give two real life examples of inertia in action (in motion and at rest)
Ex. A powerful train engine begins to pull a long line of boxcars that were sitting at rest. Since the boxcars are so massive, they have a great deal of inertia and it takes a large force to get them going. Once they are moving, it takes a large force to stop them.
Ex. On your way to school, a bug flies into your windshield. Since the bug is so small, it has very little inertia and exerts a very small force on your car (so small that you don’t even feel it).
17. What is Newton’s second law?
The net force of an object is equal to the product of its mass and acceleration, or Fnet=ma.
a. Define Fnet (or Net Force).
Force = a push or pull on an object by another object. Net Force = is the total or sum of all forces acting on an object
b. What force (magnitude only) is required to accelerate a 4 kg object at a rate of 3 m/s2?
F = ma F = (4)(3) 12N
c. What force (magnitude only) is used to stop a 6kg object with a velocity of 8 m/s stopped in 4s?
F = ma F = (6)(a) first find a a = (0-8)/4s = 2m/s2 F = (6)(2) = 12N
18. What is Newton’s third law?
For every action, there is an equal and opposite reaction.
a. If you catch a baseball in your hand, what is the action-reaction pair of forces
Your hand hits the baseball, the baseball hits your hand back.
b. If you hit a ball with a bat with a force of 10N, the ball his the bat back with a force of __10N__
19. Relationship with mass and speed. Write out equation.
Momentum(kgm/s) = mass(kg) * velocity(m/s) p = m v
20. A 10 kg book is held up in a student’s hand. The student pushes up the book with a force of 118N. What is the book’s upward acceleration?
118N Fnet is 20N
F = ma 20 = (10)a a = 2m/s2
(10)(98)=98N
21. What is the weight of a 5 kg object on the Earth? Weight = (mass)(g) (5)(9.8) = 49N
22. A 30kg object is on the floor of an elevator that is accelerating upward at 2 m/s2. Draw a force diagram and label/calculate all the forces acting on the object. Calculate Fnet and acceleration.
a is given 2 m/s2 60+98=158N
Fnet =m a Fnet = (30)(2) = 60N
(10)(98)=98N
Work, Power
23. How much work is done, when an upward force is applied to lift a 3kg object to a height of 4.2m at a constant speed?
24. A constant force of 4N is used to push a 5kg mass 12m across the floor. How much work is done on the mass in 8s?
25. What is the minimum power required to lift an 8N box 4m up in 8s?
Momentum, Impulse
26. A box with a mass of 5kg is being pulled up a hill at a constant rate of 2 m/s. What is the magnitude of the momentum of the box?
P = m v p = (5kg) (2 m/s) = 10 kg m/s
27. A 2 kg blob of putty moving at 4 m/s slams into a 6 kg blob of putty at rest. What is the speed of the two stuck-together blobs immediately after colliding?
m1 v1 + m2 v2 before = m1 v1' + m2 v2‘ after
(2.0kg)(4m/s) +(6kg)(0 m/s) = (2.0kg + 6 kg)vf
8 + 0 = 12 v 0.667m/s
28. Name 4 different safety designs on a car and on the roadway.
Seat belts/ air bags guard rails/water filled garbage cans
29. A net force of 100N acts on object A that has a mass of 25kg. The velocity is 2 m/s, what is it’s momentum?
P = m v p = (25kg) (2 m/s) = 50 kg m/s
If the object from above has the 100N force acting on it for 5s, what is it’s impulse?
Imp = Fnet t = (100N)(5s) = 500 Ns
30. A 3 kg object moving at 5 m/s collides with a 6 kg object moving in the opposite direction.
A. If both objects stop when they collide, how fast was the second object moving?
m1 v1 + m2 v2 before = m1 v1' + m2 v2‘ after
(3kg)(5m/s) +(6kg)(v) = (3kg)(0m/s) +(6kg)(0 m/s)
15 + 6v = 0 v = 2.5m/s
B. What is the total momentum of the system (both objects before and after the collision)?
P = m v p = (3kg) (5 m/s) = 15 kg m/s Before so should be 15 kg m/s after too due to the law of conservation of momentum (to check p = mv after is (6kg)(2.5) = 15kg m/s
31. Consider an 8 kg mass moving at a constant speed of 3 m/s.
A. What is the momentum of the mass?
P = mv (8)(3) 24kg m/s
B. If a 4 N force is applied to this object, for how much time must it be applied to stop the object?
Impulse = Fnet * time 24 = 4 t 6 seconds
C. What is the impulse in (B)?
Impulse is the change in momentum = 24 kgm/s
Circuits
32. What is potential difference (or voltage drop)? What does it have to do with charges?
Voltage (Potential) Difference: Electric charge flows from higher voltage to lower voltage
33. How is it possible for birds to perch on high voltage wires? When does it become unsafe for them?
Birds on the wire - No potential difference across the bird’s feet = no current J
34. When electrons flow in closed circuits do they get used up?
No they do not but the energy does
35. Give at least three examples of voltage sources.
rubbing a PVC pipe with rabbit’s fur, dry cell battery vs car battery, power supply company
36. State Ohm’s Law V = IR
the current through a circuit component is directly proportional to the voltage (or potential) across it and inversely proportional to the component’s resistance.
37. A 12 V battery is connected to a small light bulb with a resistance of 5.3 ohms. What is the current in the bulb? V = IR 12 = I (5.3) 2.26a
38. List, define, and draw examples of both series and parallel circuits. Also, list characteristics and pros and cons of each type of circuit. Series Parallel
Parallel Advantages
• The more devices (resistors) in a parallel circuit, does not decrease the current (does not dim bulbs).
• If one resistor breaks (a bulb goes out) the rest do not.
Parallel Problems
Current doesn’t stay the same for entire circuit. So energy is used up quicker. So the total current increases = faster electrons = hotter wire
b. What happens when one bulb goes out in a series circuit? What about in a parallel circuit?
Series = they all go out Parallel = only that one
c. What happens when more light bulbs are added to a series circuit? What about in a parallel circuit?
Series = they get dimmer Parallel = same strength of brightness
d. How are our houses wired? … with series or parallel circuits?
Parallel so if one goes out not everything else will go out too
39. Fill out the following equation chart regarding Series vs Parallel circuits.
Equations for Series Circuits / Equations for Parallel CircuitsVoltage / Vtot = V1 + V2 + V3… / Vtot = V1 = V2 = …
Resistance / Req = R1+R2+ R3… / 1/Req=1/R1+1/R2+1/R3
Current / Itot=I1=I2=I3 / Itot = I1 + I2 + …
40. What is the relationship between current, resistance and voltage in each type of circuit?
V = IR
– If current increases, voltage increases
• Directly proportional
– If current increases, resistance decreases
• Inversely proportional
41. What are the three main factors for resistance in a wire?
– Length of wire
• longer wires have more resistance than short wires.
– Thickness of wire
• thicker wires have less resistance than thin wires.
– Material of wire (use chart to help determine this)
• Materials with less resistivity allow electricity to flow easier
42. Define and give the equation for electric power.
rate at which electrical energy is converted into another form such as mechanical energy or light energy. P = I V
43. How much power is used by a 12 volt car battery that draws 0.5A of current?
P = I V P = (12)(0.5) 6W
44. When a charge of 15 coulombs takes 5 seconds to pass a given point, what is the current? Write out equation and show all work.
I = q/t I = 15c/5 s 3 amps
45. What is a fuse? How is it connected, by parallel or series, and why?
Fuse is connected in series. Used to shut off power as a safety precaution