unit 1 kinematics

Question 1

Scalar vs. vector

Answer 1

scalar = absolute value and MAGNITUDE (speed, distance, calories etc)
vector = direction, positive and negative depending on the problem (displacement + or -, acceleration or deceleration (+ or - acceleration), velocity, etc.)

Question 2

Is force a vector?

Answer 2

yes (5 N up or down)

Question 3

Often vectors will be indicated on variables by:

Answer 3

having an arrow above the variable (ex. a v with an arrow pointing right over it)

Question 4

mass vs. weight (and if scalar or vector)

Answer 4

Mass: scalar, absolute MATTER within an object
weight: vector, the force applied DOWNWARDS as a function of mass

Question 5

define resultant vector

Answer 5

the net vector after you’ve, like, added and subtracted the vectors along the same axis, and stuff

Question 6

When calculating resultant vector, saying, for example, north of east, is enough.
(true/false)

Answer 6

FALSE, you must have a DEGREE to describe the vector. ALSO don’t use NE, use north of east or east of north for specificity as to where the angle is from.

Question 7

Tip to tail method vs.tail to tail (parallelogram method)

Answer 7

tip to tail: draw hypotenuse

tail to tail: fill in missing sides to make a parallelogram, create median line to end of parallelogram corner

Question 8

how to subtract vectors (A-B)

Answer 8

B is negative, thus opposite direction. add A to B flipped in the opposite direction.

Question 9

what does imaginary number, i, mean in a vector?

Answer 9

turn 90 degrees toa d ifferent dimension, if you use one imaginary it goes to a different dimension, if you turn 180 degrees you go backwards, which makes it negative

Question 10

Do horizontal and vertical vectors impact each other?

Answer 10

No, regardless of the horizontal speed an object fired will remain accelerated the same by gravity

Question 11

Determine an expression for the horizontal distance traveled D in terms of H, Vx, and g (projectile launched horizontally off of a table at height H at speed V)

Answer 11

D = V*(sqrt(2H/g))

because

delta x = V0*(t)
and delta y = 1/2gt^2

Question 12

How to use components in an equation for a projectile launched at an angle

Answer 12

x = v0cos(theta)(t)
y = v0sin(theta)(t) + (1/2)gt^2

Question 13

How to find uncertainty of multiplied/divided parameters? (square with uncertain sides)

Answer 13

add/subtract uncertainties to parameters (to create the biggest/smallest result), and go with the larger calculated uncertainty (higher vs. lower) (overestimate uncertainty)

Question 14

Given a same initial velocity and height, objects fired at angles which add up to 90 degrees will move the same horizontal distance
(true/false)

Answer 14

true

Question 15

list the kinematic equations

Answer 15

v = v0 + at (no x)
x = x0 + v0x + (1/2)at^2 (no v)
vf^2 = v0^2 + 2a(x-x0) AKA delta x (no t)

Question 16

type 1 vs type 2 vs type 3 projectile motion

Answer 16

Type 1: horizontal only launch off of a given height (no angle)
Type 2: launched with an angle
Type 3: launched with an angle at a given height

Question 17

FINDING WEIGHTED AVERAGE

Question 18

definition of a force

Answer 18

interaction between two objects tending to cause acceleration if unopposed (push or a pull). these can exist without physical contact (gravity, electromagnetic, etc.) or with (tension, friction, applied force)

Question 19

units of force

Answer 19

NEWtons (N) (metric), or (kg*m)/ s^2

lbs (imperial)

Question 20

what’s the most common way to solve a physical sense problem such as:

Doesthe below equation make physical sense?
vf = ((1/2)x * t)/force

Answer 20

does it make physical sense? does lowering the force applied cause it to speed up or slow down? we know that increased time over the same distance = lower final velocity, so that doesnt makes sense, and neither does an increase in force causing lower velocity. also, the units dont make sense in velocity’s m/s if force isn’t somehow cancelled out, and with time in the numerator.

Question 21

Newton’s first law and inertia

Answer 21

object at rest stays at rest, in motion stays in motion, inertia = the resistance to a CHANGE IN MOTION of an object

Question 22

if the sum of the forces is zero, then acceleration…

Answer 22

is zero

Question 23

if acceleration is zero, then the sum of the forces…

Answer 23

is zero

Question 24

equilibrium in physics is:

Answer 24

a nonchanging velocity

Question 25

how come you can pull the rug out from an object and not move it?

Answer 25

force is effectively an accelerant across a given time, and therefore pulling the rug out from a beaker fast enough will not transfer enough force to topple it over

Question 26

Two spaceships pull cargo pods, one full and one empty. The speeds are constant, 300 m/s and 500 m/s. All masses are given in terms of M, the mass of an empty cargo pod. This is space so there are nor resistive forces. Rank the tension in the connecting cables at locations A, B, C, and D
1:
pod 2(M) —A—-pod 1(2M)——b—–engines

mSHipA = 7M
2:
pod 2(2M)—–C—–Pod 1(M)—–D—–engines

mShipB = 6M

Answer 26

None, trick question, its at a constant velocity, and with no resistive forces = engines not on = all things constant = no tension due to no fORCE

Question 26

Does newton’s 1st law hold true in every reference frame?

Answer 26

no, such as in a room if the earth stopped spinning you’d see everything accelerating for no reason but in reality it was the earth changing its velocity and decelerating . where newtons 1st law works is where ACCELERATION is zero and velocity is constant. its all about what you use to compare things, or what tREFERENCE FRAME you use

Question 27

when two ropes hold up a mass, and one is at a more horizontal angle, which one has greater tension?

Answer 27

the less horizontal one because the y component is larger compared to x, and if the x’s are equal x^2 + y^2 = c^2, if one leg is equal then the larger vertical is larger overall (and hypotenuse must always be larger than any one leg)

Question 28

two sets of ropes hold up the same mass. of the set that is more vertical and the two that are more horizontal, which have more tension?

Answer 28

the more horizontal ones, as there is more force in the x direction on top of the downward force

Question 29

when can you NOT treat object systems like single objects in regards to force of tension of rope A in stuff with like ropes A, B, C, and D?

Answer 29

when acceleration is different or in determining internal forces

Question 30

in the equation F = ma, what is the slope? how is that determined?

Answer 30

m, as that is the most physically informative when graphed. Even though other variations of that equation are correct, such as m = a/F, this would make the equation’s x, y and m values less visible

Question 31

newtons second law

Answer 31

acceleration is inversely proportional to mass, and proportional directly to NET force
a = (sum F )/m (makes sense w/cause and effect, larger force = more acceleration and more mass = more inertia = less acceleration)
or
sum F = ma
F=ma

Question 32

tips/steps of Newtons second law

Answer 32

1. Free body diagram
2. vectors —> components
3. equations of motion = + and - vectors fpr NET FORCE, larger- smaller
4. solve for unknowns

Question 33

what is friction caused by?

Answer 33

combination of two processes, imperfections in surfaces sliding across each other, and molecular forces (van der waals)

Question 34

what are the types of friction? whats the difference?

Answer 34

static vs. kinetic,

static - keeps at rest, stops something from moving until overcome
kinetic - friction during motion after static is overcome

Question 35

true/false

kinetic friction is larger than static friction

Answer 35

FALSE, STATIC is usually larger, few times it would be about the same, though probably never a situation where static is LESS

Question 36

friction equation

Answer 36

Ffriction = mu(slope, coefficient of friction) x Fn

Question 37

does mu/coefficient of friction have units?

Answer 37

nah, GENERALLY goes from 0 to 1 (more than 1 is like literally adhesive) (attribute of materials)

Question 38

does surface area, speed, or temperature impact friction or coefficient of friction?

Answer 38

no (though they CAN, our system is simplified and for this class we assume nah)

Question 39

do tires rolling on a road use kinetic or static friction?

Answer 39

static, point of contact never changes, not actively sliding without gripping (opposite of this would be like burnout or drifting)

Question 40

Kinetic vs. static friction equations

Answer 40

Kinetic: fk = Mk(Fn)
mu x Fn = constant if in motion and surfaces are sliding, regardless of acceleration or other state of motion

Static: fs <=Ms (Fn)
mu x Fn = LIMIT of static force, if you go over it starts moving, you can pull with less than that and it still shouldn’t move and thus friction is kept in equilibrium

Question 41

true/false: friction is always less than normal force

Answer 41

true, look at the equation dumbo

Question 42

what do delta x and delta y equal when a projectile is launched HORIZONTALLY (equations)?

Answer 42

Using kinematic #2: (x = x0 + v0t + 1/2*at^2)

delta x = V0*(t)

delta y = 1/2gt^2

Question 43

what is the optimal angle for a launch? is this the absolute best angle? why or why not?

Answer 43

45 degrees ONLY on level terrain. a cliff, for example, would provide extra hang time that would cause a higher horizontal velocity to be of more benefit

Question 44

kinematic equations vs. stuff like a = v/t

Answer 44

kinematics are used for INSTANTANEOUS values of variables, whereas the “other stuff” is used for AVERAGES (a(avg) = delta v / delta t)
tldr;
instantaneous points in time vs. averages with CONSTANT slopes

https://www.youtube.com/watch?v=N0TngZunzXY&list=PLPyapQSxH6mZdMBSO-_YWHYJ9DpWBxiFG&index=8