4. Physics 1

Question 1

4 questions to test concept

Answer 1

1. Can I visualize it?
2. Can I draw a picture, graph, or diagram of it?
3. Can I explain it to someone else in layman;s terms?
4. Can I think of and describe real-life examples?

Question 2

scalars

Answer 2

only magnitude, no direction

mass, temperature, speed, work, energy, charge, time, density

Question 3

vectors

Answer 3

have magnitude AND direction

velocity, displacement, acceleration, force, weight, electric field, magnetic field, momentum, impulse, torque

Question 4

a rock thrown into the air at an angle 30 degrees from the VERTICAL at a velocity of 40 m/s

Answer 4

normal equation would be x=Vcos(theta) w.r.t. to horizontal, but as it is w.r.t. vertical the eq would would be x=Vsin (theta)

Question 5

force

Answer 5

any influence capable of causing a mass to accelerate

forces are vectors

measured in newtons (N = kg*m/s^2)

Question 6

newton’s first law

Answer 6

an object as rest stays at rest, and an object in motion stays in motion, unless acted upon by an unbalanced external force

Question 7

newton’s second law

Answer 7

Fnet=ma

Question 8

newton’s third law

Answer 8

for every reaction, there is an equal and opposite reaction

Question 9

inertia

Answer 9

the ability of an object to resist a change to its velocity

Question 10

mass

Answer 10

a measure of an object’s inertia

Question 11

center of mass (center of gravity)

Answer 11

Cmass = (r1m1 +r2m2 + . . . )/mtotal

a weighted average of mass distribution

opposite is center of buoyancy - the center of mass of the fluid displaced by the submerged object (not the center of mass of the submerged object itself )

Question 12

Fnet = ma

Answer 12

1. a constant force will NOT cause an object to accelerate faster, it will cause a constant acceleration
2. a constant force can cause an object to move faster, so the displacement is changing nonlinearly, the velocity is changing linearly, and the acceleration is constant
3. a constant net force will always cause a constant acceleration, therefore a changing velocity

4.you CANNOT accelerate a ball HORIZONTALLY across the room by throwing it, as the object MUST either 1) in contact with the object creating the force, or 2) be under the influence of a field force at that exact moment.
(it can accelerate vertically as there is always the force of gravity acting upon it )

Question 13

track the velocity of a ball thrown by a pitcher - from the moment the pitcher begins his pitching motion until the ball hits the ground (no catcher, ignoring air resistance)

Answer 13

the ball experiences a force created by the pitcher that accelerates it forward, this acceleration only exists during the time that the pitcher’s hand is in actual contact with the ball. once the ball is released, it becomes a projectile in free fall. there is no acceleration in the horizontal, but there is in the vertical due to gravity. when the ball hits the ground it will have the vertical component of final velocity created by its fall from the height of release to the ground, plus the same constant horizontal velocity it had throughout the flight. (it would be in the air the same time as if it were simply dropped at the same height ex. bullet shot vs bullet dropped )

Think critically if there were to be air resistance as well.

Question 14

displacement

Answer 14

shortest distance between two points
(think velocity)
going in a circle = no displacement

Question 15

distance

Answer 15

total distance between two points
(think speed)
going in a circle = distance covered in circumference

Question 16

velocity

Answer 16

displacement / time = V

Question 17

speed

Answer 17

distance / time = V

Question 18

constant velocity/ constant speed

Answer 18

1. no acceleration
2. no net force
3. all forces sum to zero
4. no change in direction
5. the object is in equilibrium

Question 19

acceleration

Answer 19

any change in velocity/second

(you accelerate when you walk around a corner because velocity is a vector with both changing magnitude and direction, thus constitutes in acceleration)

Question 20

1. if there is no net force, can there be acceleration?
2. if the force increases, what happens to acceleration?
3. if there is no acceleration is, or could there be, a force?

Answer 20

1. if there is no net force, there can never be acceleration (2nd law)
2. if forces inc. acceleration inc., if forces inc linearly, acceleration inc. linearly, if force inc. exponentially, acceleration increases exponentially.
3. if there is no acceleration, there could be a force acting on that object, however if there is a force we would know that it must be exactly canceled out by other force vectors on that same object (the other object must be in equilibrium)

Question 21

Linear Motion Graphs

Answer 21

1. What does the slope represent?
2. Is the slope (+) or (-)?, what does the sign of the slope tell you?
3. Is the slope constant (straight line) or non-constant (curved line)? what does this observation tell you?
4. What value is on the y-axis?
5. Is the y value (+) or (-) (i.e. are you above or below the x-axis? What does this observation tell you
6. Do you expect the value on the y-axis to be large or small at t=0

Question 22

velocity vs. time graphs

Answer 22

1) Crossing the x-axis means velocity went from positive to negative; in other words, the particle turned around.;
2) A corner (where slope abruptly changes from positive to negative or vice versa) tells us that the direction of the acceleration vector abruptly reversed;
3) A horizontal line tells us that acceleration is zero (because slope is zero) and that velocity is constant.

Question 23

displacement vs time graphs

Answer 23

1) Crossing the x-axis means that we passed the origin;
2) A corner tells us that the sign of velocity (which is the slope of a d vs. t graph) abruptly changed— in other words, the object turned around [NOTE to your students that this is entirely different from a velocity vs. time graph where the action of “turning around” is indicated by crossing the x-axis];
3) A flat line tells us that displacement is constant, which means the object is standing still. It also tells us that velocity is zero because the slope of the line is zero—another proof that the object is not in motion at that instant.

Question 24

if a projectile has an initial vertical velocity of 30 m/s, how many seconds will it take to reach its max height?

Answer 24

3 m/s

Question 25

if a projectile has an atoll velocity of 60 m/s at an angele 30 degrees from the horizontal, how many seconds will it be in the air?

Answer 25

find vertical component of velocity = 60sin(30) = 30 m/s 30m/s horizontal is 3 seconds to max height (halfway points) so = 6 seconds in the air total

Question 26

Vavg

Answer 26

average velocity = Vavg = (V1+V2)/2

Question 27

if a projectile has a vertical velocity of 100m/s, how many seconds will it be in the air?

Answer 27

it takes 10 seconds to reach max height, | so avg V will be 50 m/s

Question 28

distance traveled

Answer 28

distance = rate * time

Question 29

if a projectile has an initial V of 30m/s, how long will it be in the air, how high will it go, and what will be its avg velocity during the entire trip?

Answer 29

3 seconds for max height --> so 6 seconds in air total avg velocity will be 15 m/s --> so max height is 45meters avg velocity entire trip = displacement/ time = 0

Question 30

projectiles

Answer 30

falling bodies in two dimensions separate into x and y components horizontal component = distance traveled = range = Vx *time think: 1. horizontal V never changes (w/ no air resistance) 2. horizontal acceleration always = 0 3. vertical acceleration always = 10m/s downward 4. vertical behavior is exactly symmetrical (upward and downward trips are identical) 5. time in air is dependent on the vertical component of velocity only 6. range depends on both the vertical and horizontal components as vertical component dictates time and the horizontal component dictates range. 7. time is always the same for both x and y components of the motion

Question 31

compare a bullet was shot straight up from atop a cliff to a bullet shot straight down from a cliff, what is the final velocity of each bullet as it hits the ground?

Answer 31

the velocities are the same, as the bullet shot up will reach zero, where it then falls back down and should have the same velocity by the time it reaches back to the height it was shot at, thus giving the same initial velocity

Question 32

two students throw identical balls into the air with identical initial total velocities of 40m/s. First student throws it at 50 degrees, and second student throws it at 40 decrees. what will happen?

Answer 32

first students ball will be in the air longer, but travel the same distance the larger the vertical velocity, the larger the time in the air max horizontal distance = at 45 degrees, both velocities varied by the same |5| magnitude so distance is the same

Question 33

x = 1/2at^2

Answer 33

not relationship

Question 34

V = sqrt(2gh)

Answer 34

will work for both Vi and Vf as projectiles go begin and end with the same velocity

Question 35

tair = 2V/g (V= Vxi)

Answer 35

used only to calculate "round trip" times, or in other words, the total time in the air

Question 36

air resistance

Answer 36

1. cross section area: greater cross-section ara impacting the air = more are resistance 2. shape: less aerodynamic - more air resistance 3. velocity: increased velocity = more air resistance note: always assume air resistance is being ignored, unless it specifically states otherwise in the question stem or passage.

Question 37

terminal velocity

Answer 37

mg = Fair object has stopped accelerating, and forces of gravity = force of air resistance note: objects in vaccum do not have a terminal velocity as there is no air resistance

Question 38

gravity

Answer 38

is a field that exists between any two objects with mass

Question 39

universal law of gravitation

Answer 39

F= Gm1m2/r^2 --> simplified to F=mg as g = Gm1/r^2 G = gravitational constant = 6.67x10^-11 m^3/kg*s^2 note: all forces are equal and opposite in a stationary object (human put as much force on earth, as earth puts on human)

Question 40

Potential energy

Answer 40

on earth PE = mgh in space PE = -Gm1m2/r note: (-) sign is needed as without it r inc, PE dec.

Question 41

friction

Answer 41

opposes sliding, not motion if there is sliding = kinetic friction, if not than static friction

Question 42

kinetic friction

Answer 42

Ff = (mu)k Fn = (mu)k mgcos(theta)

Question 43

static friction

Answer 43

Ff = (mu)s Fn = (mu)s mgcos(theta)

Question 44

force down an incline plane, parallel to surface

Answer 44

F = m g sin(theta)

Question 45

normaal force on an inclined plane

Answer 45

Fn = m g cos(theta)

Question 46

velocity of a particle at the base of an inclined plane

Answer 46

Vf = sqrt(2gh)

Question 47

acceleration down an inclined plane

Answer 47

a = g sin(theta)

Question 48

what is the tension in a rope being pulled from opposite ends with identical 50N forces?

Answer 48

it is 50N. (same as rope attached to a wall or ceiling)

Question 49

a 500 kg elevator is being accelerated upward by a cable with a tension of 6000N. what force does the elevator exert on the the cable?

Answer 49

according to newton's third law the elevator cable us pulling on the elevator with 6000N of force, the the elevator must be pulling on the rope with a force of 6000 newtons (same as tension on both sides of rope but vertically)

Question 50

hooke's law (springs)

Answer 50

F = k (delta)x ((delta)x is displacement of the spring from its equilibrium point, not length of the spring) multiple springs use: 1/keffective = 1/k1 + 1/k2 + 1/k3

Question 51

A student hangs a 4kg mass on a spring and it stretches 1m. What is the spring constant and how far will the spring stretch if he attaches a 2kg mass?

Answer 51

F=mg=k delta x | -> k=mg/delta x = 4kg*10m/s^2 / 1m

Question 52

elastic potential energy

Answer 52

energy stored in a compressed spring PE=1/2 k delta x^2 note: normally used with conservation of energy with a mass traveling at a certain velocity hitting a spring (1/2mv^2=1/2 k delta x^2)

Question 53

spring compression and kinetic energy

Answer 53

a ball moving with twice the kinetic energy CANNOT compress a spring twice as far, but a ball moving with twice the Velocity CAN compress a spring twice as far

Question 54

pendulum (energy)

Answer 54

PE is at maximum when at max height of arc and minimum is at the lowest of the arc KE is at maximum when the pendulum is at the bottom of the arc and the minimum is at the max of the arc note; gravitational potential energy is 0 at the lowest point of the arc (when h=0, PE = 0)

Question 55

pendulum movement

Answer 55

one cycle is a movement from 1 side to another, and back to the original position the reasons why pendulums slow down is due to non conservation of energy such as air resistance

Question 56

simple harmonic motion

Answer 56

anything representing a sin wave, anything that socialites back and fourth ``` T = 2 pi sqrt(m/k) [mass on a spring] T = 2 pi sqrt(L/g) [pendulum] ```

Question 57

mass-spring systems

Answer 57

inc mass = dec frequency, length of spring has no effect on frequency, the mass of the spring itself also has no effect on frequency, increasing gravity also has no effect, increasing the spring constant will also increase frequency

Question 58

pendulum systems

Answer 58

decreasing mass will have no effect, decreasing long of pendulum will inc. frequency, dec. gravity will dec. frequency

Question 59

density

Answer 59

D = m/v water density: 1000kg/m^3 = 1g/cm^3

Question 60

specific gravity

Answer 60

how dense something is compared to water SG = Dsubstance/Dwater note: for objects floating in liquids, the fraction of the object submerged = ratio of the density of the object to the density of the liquid

Question 61

a ball is floating 3/4 submerged in a liquid with a density of 2g/cm^3. what is the specific gravity of the liquid and density of the ball?

Answer 61

Because the ball floats with 3⁄4 of its volume submerged it must be 3⁄4 as dense as the liquid. Therefore the density of the ball must be 1.5g/cm3. This is 1.5 times as dense as water so the SG of the ball is 1.5, and the SG of the liquid is DLiquid/DH2O=(2g/cm3)/(1g/cm3)=2.

Question 62

archimedes principle

Answer 62

any object displaces an amount of fluid exactly equal to its own volume note: the weight of the displaced fluid is exactly equal to the buoyant force pushing up on the object

Question 63

buoyant force

Answer 63

Fbuoyant = rho v g rho = p = density of the fluid, not the object v= volume of the fluid displaced note:depth and mass has no change in buoyant force

Question 64

apparent weight

Answer 64

apparent weight of a submerged object is the actual weight minus the buoyant force apparent weight = actual weight - Fbuoyant AW = aW -Fbuoyant

Question 65

general pressure formula

Answer 65

``` P = F/A units = Pa, mmHg, atm, Torr ``` atmospheric pressure = pressure do to atmosphere fluid pressure = pressure of fluid on an area gauge pressure = pressure measured with respect to atmospheric pressure, where atmospheric pressure is defined as zero gauge pressure (basically pressure in excess of ambient atmospheric pressure)

Question 66

fluid pressure formula

Answer 66

P = rho g h

Question 67

pascal's law

Answer 67

pressure is transmitted in all directions, undiminished, through a contained, incompressible fluid (if you increase pressure in a confined incompressible fluid, it increases by that same amount in every other point within that fluid)

Question 68

flow rate

Answer 68

Q = A V A=total cross-section area (cardiac output = stroke volume * heart rate) cross sectional area decreases as you go from aorta to capillaries, thus velocity is slowest at capillaries

Question 69

Bernoulli's equation

Answer 69

K = P + rho g h + 1/2 rho v^2 if fluid velocity increases, pressure decreases note: commonly used for velocity of water exiting a spigot

Question 70

surface tension

Answer 70

intensity of intermolecular forces per unit length at the surface of a liquid

Question 71

capillary action

Answer 71

cohesive vs. adhesive forces

Question 72

cohesive forces

Answer 72

forces between the fluid molecules

Question 73

adhesive forces

Answer 73

forces between the fluid and the container

Question 74

a 20 kg block of unknown density has an apparent weight of 150 N when fully submerged in a liquid with a density of 8g/cm^3. what is the density of the unknown object?

Answer 74

the 20 kg block will create a 200N force outside of the liquid and 150N in the liquid. the 50N difference is due to the buoyant force acting up on the object. therefore the actual weight is 4 times as dense as the buoyant force. multiply density of the fluid by the factor of 4 to get 32 g/cm^3 as the density of the unknown object.