Physics 1 Flashcards
(87 cards)
0
Q
Is mass a vector or scalar?
A
Scalar. It only shows magnitude
1
Q
Whats the difference between a vector and a scalar?
A
Vectors have both magnitude and direction. Scalars just have magnitude.
2
Q
Temperature a vector or scalar?
A
Temp is a scalar. Only shows magnitude
3
Q
Is velocity a vector or scalar?
A
Velocity is a vector it shows magnitude and direction.
4
Q
Is speed a vector or scalar?
A
Scalar, it only shows direction.
5
Q
Is displacement a vector or scalar?
A
Displacement is a vector it shows magnitude and direction.
6
Q
Is acceleration a vector or scalar?
A
Vector shows magnitude and direction
7
Q
Is force a vector or scalar?
A
Force is a vector. It shows magnitude and direction…. Think of If you’re forcing something with a magnitude in a certain direction.
8
Q
Is work a vector or scalar?
A
Work is a scalar. It says nothing about direction. It just gives a magnitude. Ex work is energy expended and energy is a scalar.
9
Q
Is energy a scalar or vector?
A
Energy is a scalar. It has nothing to do with direction.
10
Q
Is weight a vector or scalar?
A
weight is a vector. It has a magnitude and direction. Mass would be the scalar form.
11
Q
Is charge a vector or scalar?
A
charge is a scalar. It has nothing to do with direction.
12
Q
Are electric and magnetic fields vectors or scalars?
A
They are vectors. Think of a magnet, it has a field around it that is supplying a force to another object.
13
Q
Is momentum a vector or scalar?
A
Momentum is a vector. It is a product of a vector times a scalar. p=mv
14
Q
Is impulse a vector or a scalar?
A
Impulse is a vector. It is an applied force for a given amount of time. So it essentially is just a force for a certain amount of time.
15
Q
Is density a vector or scalar?
A
density is a scalar. It is just a quantity that has no implication in the form of direction. It basically just has to do with the amount of condensed mass.. so very similar to mass
16
Q
Is Torque a vector or scalar?
A
Torque is a vector. It is a force in the circular motion. Someone using a wrench to undo a bolt would be torque.
17
Q
What is a vector made up of?
A
Two components one along the x axis and one along the y axis. Think of the dog getting his collar pulled at a 45 degree angle. If we replace that with pulling straight up and straight to the right the dog wont know the difference and these two different ways are equal to each other.
18
Q
when adding vectors, can you use pythagreons theorem when two vectors don’t form a 90 degree angle?
A
No, you cant the vectors have to form a 90 degree angle.
19
Q
When multiplying two vectors and the answer is a scalar or dot product ie like Work. What must you also multiply by?
A
cosø where theta is the angle between the two vectors.
20
Q
If you are multiplying two vectors and the answer is a third vector. or cross product (e.g. torque) what must you also multiply by?
A
Sinø, torque= Frsinø
21
Q
Is the product of two vectors always always a vector?
A
No, take Work and Torque for example. Work is the product of two vectors but is a scalar. And torque is two vectors but the product is a scalar.
22
Q
Is the product of a scalar and a vector always a vector?
A
True, for example F=ma
23
Q
What is the resultant of a vector?
A
It is the sum of two vectors which have been added by the head and toe method and this the third vector.
24
what if you and someone else were to push on a car on each side of the car with equal force?
The car would stay stationary even though there is a great amount of force being exerted on the car. Imagine this as two vectors if one pushes a little harder than the other the car will move.
25
Imagine what the velocity, displacement, and acceleration vectors would look like for a ball that has been tossed up in the air. Ignoring air resistance.
Think about it, the velocity vector is going to keep getting smaller because the acceleration due to gravity is always pointing in the downward direction. The acceleration vector is going to be the same the whole time just pointing downward due to gravity. And the displacement each vector will get bigger but when the ball is caught the first vector and last will be the same.
26
What does the velocity and displacement and acceleration vectors look like for a car traveling around a track?
?
27
What does the acceleration and velocity vectors look like for a ball oscillating on a string?
?
28
What are the 4 questions of conceptual mastery?
Can I visualize it? Can I draw a picture, graph or diagram of it? Can I explain it in layman's terms? Can I think of and describe real life examples?
29
What is Force?
Any influence capable of causing a mass to accelerate. Forces only exist as a result of an interaction.
30
What are the units for a Newton? Hint use F=ma
kg m/s^2
31
What are the two broad categories that Forces can be placed under. Give some examples of each.
Contact Forces- When two objects are physically touching each other. Frictional, Normal, Tension, Air resistance force
Action at a distances- forces that occur when two object aren't in physical contact with each other. Yet the still exert a push or pull. Gravitational, Electrical, Magnetic forces.
32
Describe what an applied force is?
A force exerted by an object or a person to another object. Example a person pushing a desk across a room.
33
Explain the Force of gravity?
The force of which the earth, moon or an other massive object attracts and object towards itself.
The Force of gravity or Weight= mass*gravity
34
What is Normal Force?
Its the support force exerted when an object is in contact with another stable obeject.
Ex. A book resting on the counter has a normal force upward.
A person leaning against a wall has a normal force that is perpendicular with the wall.
35
What is Frictional Force?
A force exerted by a surface as an object tries to move across it or makes an effort to move across it.
Ex. A book sliding down a inclined table.
36
What is air resistance?
A type of frictional force that acts upon an object as it moves through the air.
Ex. A skydiver experiences air resistance
37
What is tension force?
A type of force that is transmitted through a rope string or cable of some sort when it is pulled tight by some force acting from the other end.
Ex. A mass hanging from a cable that is attached to a roof.
38
What is a spring force?
A force that is exerted by a compressed or stretched string upon any object that is attached to it.
Ex. A mass pushing down on a spring, the spring exerts a force in the opposite direction.
39
What does Newton's first law state (the law of inertia) ?
And object at rest stays at rest, and an object in motion stays in motion at the same speed and in the same direction unless acted upon by an unbalanced force.
40
What is inertia?
The ability of an object to resist a change to its velocity or motion.
41
what is mass?
Mass= a measure of an objects inertia
42
describe why if you throw a ball horizontally it will eventually stop even though Newton's first law says that and object will stay in motion unless acted upon by an unbalanced force?
The ball eventually comes to rest because there are unbalanced forces acting upon it like gravity which will cause it to come to rest.
43
what is center of mass? And what is the equation?
a weighted average of mass distribution. The average location of all the weight of an object.
Cmass=(r1m1+r2m2+r3m3....)/mtotal
44
Explain how you would use the center of mass equation?
Choose a reference point, and from there you determine each displacement vector. If you choose the center of mass as one object as the origin, one of the terms will drop out of the equation.
45
What is an example of center of mass that explains this concept well.
Think of a square block. The center of mass is right in the middle so you can balance this on your finger if you stick it right under the COM. If you add a quarter to the left side of the block this will cause the center of mass to switch and be more directed to the left and you will need to position your finger differently in order to balance the block.
46
Explain what the center of buoyancy is?
it is at the center of mass of the fluid displaced by the submerged object. ( Not at the center of mass of the submerged object itself). Think of the animation you did. Its basically the center of mass of the submerged portion of the object. Think about the Kayak video on youtube. Watch it if don't get it.
47
What is Newton's second law?
The ACCELERATION of an object is dependent upon two variables, the mass and unbalanced net force.
Remember forces do not cause motion, they cause acceleration. You can have balanced forces like Normal Force and Weight but the object could still be in motion. Like the sledder going down the hill with no friction will remain with constant velocity.
48
The Mcat will try and make problems sound difficult, but they are siimple. When asked for force mass or acceleration try using F=ma first.
Just a note.
49
- Will a constant force cause an object to accelerate faster and faster?
- Does a change in Force cause a change in acceleration?
- Does a constant force cause an object to move faster and faster?
- Does a constant force cause a constant velocity
- No it will cause a constant (non changing) acceleration. Constant accel is the measure of continuing increase of velocity per unit of time. Car from 30 to 40 mph in 5 sec and then from 40 to 50 in 5 secs is constant accel. So NO.
- Yes
- Yes a constant force will cause the velocity to increase faster and faster as in the example above, it just wont change its acceleration.
- No, the object will move faster and faster.
50
- Can you accelerate a ball horizontally across a room by throwing it?
- Is the ball accelerating in the vertical direction?
- No, the ball will only accelerate when in contact with object creating the force (ie hand) or under the influence of a gravitational or electric/magnetic field.
- Yes, gravity is always causing an acceleration once the ball leaves the hand.
51
Track the velocity of a ball thrown by a pitcher from the time the picture begins his windup until the ball hits the ground. ( no air resistance)
The ball will only accelerate horizontally when in contact with the hand of the picture. Once the picture lets go, the ball will move horizontally will the same velocity but the vertical acceleration of gravity will cause the ball to hit the ground.
52
Track the velocity of a cannon shot through the air with wind resitstance.
The ball will gradually loose velocity and eventually hit the ground due to gravity.
. . . . . . . . . . .
53
Explain Newton's third law of motion? Provide some examples
-whenever one object exerts a force (ie contact or a field) on a second object, the second object always exerts an equal and opposite force on the first object.
- a baseball hitting a bat. The baseball will cause a force on the bat but the bat will cause an equal force propelling the baseball forward.
- When a brick is dropped from a very high height. A force is exerted on the object by earths gravitational field to cause an accleration. However the brick is creating an equal force on the earth and causing an acceleration, we just don't notice because the earth is so much more massive.
54
Explain the force of gravity between the Sun and Earth regarding
Newton's third law.
The force the Earth exerts on the Sun is equal in magnitude to the force the Sun exerts on the Earth, however the Sun is very much more massive than Earth. So, this force will affect Earth much more than the Sun. Earth, and other planets, therefore orbit the Sun, which remains nearly stationary. Mutual gravitational forces accelerate the less massive object more. It is the same reason why we fall down towards the Earth, and the Earth does not fall up towards us.
55
Explain the difference between distance and displacement? Give examples
- DISTANCE is how much ground an object has covered during its motion, and DISPLACEMENT is how far out of place an object is or the objects overall change in postion.
- Indy 500 the cars displacement at to end of the race is 0 but distance is 500.
56
Can you use D=rate*time to calculate displacement?
No this will give you distance not displacement.
57
Whats the difference between velocity and speed? Give Examples
SPEED is how fast an object is moving, and VELOCITY is the rate at which an object changes postion.
-If a person rapidly takes one step forward and one step back this would result in a zero velocity. Speed is just the rate at which an object covers a distance.
Ave speed=distance/time Ave velocity=displacement/time
58
When on the MCAT can we treat speed and velocity the same?
IF and only if the question makes it clear that the distance traveled is along a straight line.
59
What should you think of when you see "Constant Velocity" or "Constant Speed"?
1. No Acceleration 2. No net force 3. All forces sum to zero ( up forces=down forces, left forces=right forces)
4. No change in direction 5. No change in equilibrium
60
What is acceleration?
The rate at which an object changes its velocity. An object is accelerating if it is changing its velocity.
Ave acceleration=∆v/t
61
If a car is slowing down what direction would its acceleration vector point?
It would point in the opposite direction of its motion.
62
Do you accelerate when you walk around a corner at constant speed? If yes explain
Yes you do accelerate, remember acceleration is a change in velocity over a time. When you walk around a corner the magnitude of the velocity vector might not be changing but the direction of the velocity vector is changing.
63
If there is no net force could there be an acceleration?
If the force increases what happens to acceleration?
If there is no acceleration could there be a force?
- No Net Force=m*a
- Acceleration increases as well
- There could be forces canceling each other out like two people pushing on a box but this means no net force therefore accel is 0.
64
A position vs time graph what does the slope tell us?
Whatever characteristics the velocity has, the slope will exhibit the same (and vice versa). If the velocity is constant, then the slope is constant (i.e., a straight line). If the velocity is changing, then the slope is changing (i.e., a curved line).
65
A velocity vs time graph what does the slope tell us?
- Acceleration
- One knows an object is moving in the positive direction if the line is located in the positive region of the graph (whether it is sloping up or sloping down). And one knows that an object is moving in the negative direction if the line is located in the negative region of the graph (whether it is sloping up or sloping down). And finally, if a line crosses over the x-axis from the positive region to the negative region of the graph (or vice versa), then the object has changed directions. Look in MCAT journal for drawings
66
what does the sign of the slope on a graph tell us?
For a displacement vs time graph the if the slope is positive (line moving upwards) then the object is moving to the right.
For a velocity vs time graph since the y axis is velocity if the graph line lies below the x axis then the object is moving to the left. If the line lies above the x axis then its moving to the right. (+ and - velocity)
67
- What does the sign of the slope on a velocity vs time graph tell us?
- Does it tell you the direction in which the particle is moving?
- The slope on a velocity vs time graph tells us whether we have a positive or negative acceleration.
- No tells us whether object is slowing down or speeding up
- If slowing down the acceleration vector will always point opposite to the velocity vector.
68
On a displacement vs time graph what does a constant slope tell us and what does a curved slope tell us?
A constant slope tells us that the object is moving at constant velocity. If the line starts to curve this means that the object is speeding up so there is acceleration.
69
If we see a flat line on the y axis of both position and velocity vs time graphs what does that mean?
On a displacement vs time graph that means the displacement is constant so the object isn't moving
On a velocity vs time this means the velocity is constant
70
What does it mean if your above or below the x axis on a displacement and velocity vs time graph?
Displacement- above means object is to the right of the origin, and below object is to the left of the orgin
Velocity- this tells us whether the object is moving to the right (above) or to the left (below) x axis
71
For a velocity and displacement vs time graph describe what happens to the particles motion in each scenario. 1) the line crosses the x axis 2) the lines forms a sharp corner 3) the line is perfectly horizontal
1) displacement - if it was to the right of the origin its now moving to the left of the orgin. Velocity- the object now has a negative velocity so moving forward but now is moving backward.
2) displacement- now moving with the opposite sign of velocity. Velocity- now has the opposite sign of acceleration.
3) displacement- object is not moving (stays at same position) Velocity-moving with constant velocity
72
If a projectile has an initial velocity of 30 m/s, how many seconds will it take to reach its max height?
3 seconds, gravity has an acceleration of 10m/s/s
73
If a projectile has an initial vertical velocity of 60 m/s at an angle of 30 degrees from the horizontal, how many seconds will it be in the air?
6 seconds, the y component is equal to 60*sin30 which is 30 m/s. 3 seconds to go up 3 seconds to come back down.
74
How do you find the average velocity?
- take the initial velocity + the final velocity and divide it by 2.
- initial + final / 2
- only consider the upward half or downward half of the motion and one will always be 0
75
If a projectile has an initial vertical velocity of 100 m/s, how many seconds will it take to reach the max height and what is its average velocity?
it will take 10 seconds and the average velocity is 50 m/s 100+0/2
76
how do you find how high an object travels in projectile motion problems?
Take average velocity (rate) and multiply it by the time and this will give you your height. distance= rate*time
77
If a projectile has an initial vertical velocity of 30 m/s, how long will it be in the air, how high will it go, and what will be its average velocity during the entire trip?
it will be in the air for 3 seconds, it will go 45 m, and the average velocity is 15 m/s
78
How do you solve for range (distance traveled in x direction) for projectile motion problems?
Split problem into component vectors, find x component velocity and multiply it by the time of flight of the object ( so how long it takes to go up and come down) Range=Vx*time
79
Name some things you should think of in projectile motion problems?
1) Horizontal velocity never changes, 2) Horizontal acceleration always=0, 3) Vertical acceleration always = 10m/s/s downward, 4) Vertical behavior is symmetrical ( i.e., the upward trip is identical to the downward trip), 5) Time in air depends on the vertical component of velocity only, 6) Range depends on vertical and horizontal component because time in air and horizontal velocity must be multiplied 7) time is always the same for both x and y components of motion.
80
If a man on a cliff first fires a gun straight down toward the ground below ; and then fires a second round straight up into the air, which bullet will hit the ground with the greater velocity?
They will hit at the exact same velocity. When he fires the bullet up with an initial velocity it will have that exact same velocity when it reaches the point from where he fired it from. Then from there as both drop they will each have the same initial velocity.
81
What angle gives the greatest distance in projectile motion?
45 degrees from the horizontal will give the object the greatest range.
82
what equation do you use to find final velocity? And when do you use it?
V=√(2gh)
| Use this when asked for final velocity from a given drop height.
83
What are the 3 equations you need to memorize for projectile questions?
X=1/2at^2 V=√(2gh)
tair =2V/g this is used to calculate the total time in the air, V
must be the vertical component of initial velocity
84
why can you use V=√(2gh) to find initial velocity as well?
Because say for a projectile motion the object when coming down will reach the same final velocity as the initial
85
what factors affect the magnitude of air resistance?
Surface area of object falling, Velocity.. the greater the velocity the more air resistance.
86
what does it mean when something is said to be at terminal velocity?
The force of the objects weight and the force of the air resistance are balanced, therefore there is no more acceleration.
