Physics Review
You are riding in a car on a straight stretch of a two-lane high- way with a speed of 26 m>s. At a certain time, which we will choose to be t = 0, you notice a truck moving toward you in the other lane. The truck has a speed of 31 m>s and is 420 m away at t = 0. (a) Write the position-time equations of motion for your car and for the truck in the other lane. (b) Plot the two equations of motion on a position-time graph. (c) At what time do you and the truck pass one another, going in oppo-site directions? This is on pg 62 #39-know
(a). car: xf = 0 + 26m/s(t) truck: 420m - 31m/s(t)
A polar bear walks 2 mi N, 4 mi E, 4 mi W, 3 mi S. He completed his trip in 4 hrs find his speed and velocity- on test
- - - - - - - - - - - -> | <----------------- | | | | | | | | | | \/ this is a bad visual ^^ Total distance is 2 mi + 4 mi + 4 mi + 3 mi = 13 mi Displacement is Δx = xf - xi Δx = 3 mi - 2 mi = -1 mi S speed = distance / time s = 13 mi/ 4hr = 3.25 mi/hr velocity = Displacement Δx/ time v = -1 mi / 4hr = -.25 mi / hr south
Different Slope Meanings A line going up and to the right =? A line going down and to the left =? A horizontal line =?
A line going up and to the right has a positive slope and a positive velocity A line going down and to the left has a negative slope and a negative velocity A horizontal line has zero slope and zero velocity
Define Science- on test
An organized way of thinking about nature and understanding how it works - process - constantly evolving/developing - cannot be predicted - seeks explanation - not a collection of facts, its an explanation of understanding nature
Atomic Physics- be able to recognize the diff types of physics them/name 2
Atomis Physics- structure of atoms, development of small electronic componants
An athlete sprints 50.0 m in 6.00 s, stops, and then walks slowly back to the starting line in 40.0 s. If the direction of the sprint is taken to be positive, what are (a) the average sprint velocity, (b) the average walking velocity, and (c) the average velocity for the complete round-trip? This is on pg 51 exercise 2.5- on test
Average velocity = Displacement/time Average velocity sprint = 50.00 m-0/6.00 s = 8.33m Average Velocity walk = 0-50.00 m/40 s = -1.25 Average Velocity for entire trip = 0-0/ 46-0 = 0/46 = 0m/s
Average Speed Equation - on test
Avg. Sp. = total distance/ total time
Average Velocity Equation- on test
Avg. Vel. = total displacement/total time
What are Base Units- on test
Base Units- standard "measuring stick" for a physical quantity base units are made up of SI units
Bias- on test
Bias- a preference for a particular view of a person rather than logical or scientific reasons -important to see through bias - make informed decisions
Quantity Distance =? Area (A) =? Volume (V) =? Velocity (v) =? Acceleration (a) =?
Dimention Distance = L Area (A) = L^2 Volume (V) = L^3 Velocity (v) = L/T Acceleration (a) = L/T^2
Define Displacement- on test
Displacement - the change in position of an object -can be + or - - Vector -direction often indicated by its sign - can be suplimented wiht a named direction
The distance from math class to music class is 6.0 m and the distance from music class to the library is 14.0 m find distance and displacement- on test
Distance is 6.0 m + 14.0 m = 20.0 m Displacement Δx = xf - xi Δx = 14.0 m - 6.0 m = 8.0 m
The distance from math class to the library is 8.0 m and the distance from the library to physics class is 5.0 m find the distance and displacement- on test
Distance is 8.0 m + 5.0 m = 13.0 m Displacement Δx = xf - xi Δx = 5.0 m - 8.0 m = -3.0 m
Distance- on test
Distance- the total length of a path that is taken on a trip -SI unit (m) -scalar
Explain Expirimentation (3rd step in Scientific Method)- on test
Expirimentation- you test out your hypothesis, can support or reject hypothesis
Explain Hypothesis (2nd step in Scientific Method)- on test
Hypothesis- detailed scientific explanation for a set of observations it can be verified, rejected and revised
Explain Infurence (2nd step in Scientific Method)
Inference- logical interpritaion of observations
Laser physics- be able to recognize the diff types of physics be able to name 2
Laser physics- ultra pulses of light to cool atoms
Medical Physics- be able to recognize the diff types of physics them/name 2
Medical Physics- X-Ray, radiation, chemotherapy and imaging
Nuclear Physics- be able to recognize the diff types of physics them/name 2
Nuclear Physics- provides info about sorces within atoms, critical to understanding the universe
Explain Observation (1st step in Scientific Method)- on test
Observation - *described through senses*, be creative about it ex: how does the object move does it speed up or slow down does it move straight or curved does it start/stop or move constantly
Optical Physics- be able to recognize the diff types of physics and be able to name 2
Optical Physics- cameras and communication improve in astronomy -poineered by Galileo and Newton
Physical Quantity
Physical Quantity- a property of a physical system that can be measured v= speed d= distance t= time v= d/t d= vt t= d/v
What are SI units- on test
SI unit- base unit of meter (m), kilogram (km), and seconds (s) -Length (L) -Mass (M) -Time (T) prefixes modify SI units
Scalar- on test
Scalar- magnetude only
A bowling ball moves with constant velocity from an initial posi- tion of 1.6 m to a final position of 7.8 m in 3.1 s. (a) What is the position-time equation for the bowling ball? (b) At what time is the ball at the position 8.6 m? This is on pg 59 #36-know
The equation is xf= 1.6m + (2m/s)(3.1s) to find v you do 7.8-1.6/ 3.1 = 2m/s 8.6m = 1.6m +(2m/s)(t) subract 1.6m from both sides and you get 7 = (2m/s)(t) divide 2m/s from both sides and you get t = 3.5 s
Difference between theories and laws- on test
Theories- are well supported EXPLANATIONS of nature Laws- are well supported DESCRIPTIONS of nature There are more thoeries than laws
Theory - on test
Theory- a detailed explanation of some aspects of nature that account for a set of well tested hypothesis
Four trains travel on different sections of a long straight track. Taking north to be the positive direction, rank the trains in order by velocity, from most negative to most positive. The trains move as follows: Train A moves north with a speed of 10 m>s. Train B heads south and covers 900 m in 1 min. Train C also heads south and has twice the speed of train A. Train D travels north and covers 24 m in 2 s. This is on pg 52 #17- on test
Train A has a speed of 10m/s Train B has a speed of -15m/ Train C has a speed of -20m/s Train D has a speed of 12m/s The ranking would be C, B, A, D
Vector- on test
Vector- magnitude with a direction
You ride your bicycle 1 km at 10 km>h and then another 1 km at 30 km>h. Is your average speed for the total 2-km trip greater than, less than, or equal to 20 km>h? This is on pg 50 exercise 2.4- on test
You first need to find how long it took them to bike the 1 km at 10 km>h and 1 km at 30 km>h s = d/t 10 km/h = 1 km/t convert to seconds t = 360 s 30 km/h = 1 km/ t t = 120 s average speed = total distance/total time AS= 2 km/ 480 s AS = 15 km/h
The mass of a newborn baby's brain has been found to increase by about 1.6 mg per minute. (a) How much does the brain's mass increase in 1 day? (b) How long does it take for the brain's mass to increase by 0.0075 kg?
a.) 1.6 mg/min * 1440 min/1 day = 2304 mg/day b.) 2304 mg/day -----> 0.0075 kg 2.304g/day ----> 7.5 g 7.5 g/2.304 g = 3.3 days
A finch rides on the back of a Galapagos tortoise, which walks at the stately pace of 0.060 m>s. After 1.2 minutes the finch tires of the tor- toise's slow pace, and it takes flight, traveling in the same direction for another 1.2 minutes at 13 m>s. What was the average speed of the finch over the entire 2.4-minute interval?-know
first we need to find the distance of the finch's trip d=t(s) d(1) = (1.2 min/1 *60 sec/ 1 min) (0.060 m/s) = 4.32 m d(2) = (13 m/s) * (1.2 min/1 *60 sec/ 1 min) = 936 m Average Speed = total distance/ total time AS = 940.32 m/ (2.4 min/1 * 60 s/1 min) = 6.5 m/s
Peer Review- on test
reports are sent to experts in the field so they can look for error, bias, oversight
How far in km can a kangaroo hop in 3.2 min when its speed is 65 km/hr How much time will it take the kangaroo to hop 0.25 km in seconds -know
s = d/t d = t*s 3.2 min/1 * 1 hr/60 min = 0.05 hr d = (0.05 hr)(65 km/hr) = 3.3 km t= d/s t = 0.25 km divided by 65 km/hr = 0.00385 hr 0.00385 hr/1 * 3600 s/1 hr = 13.86 s
What is the speed equation what is the definition- on test
speed = distance / time speed- the rate of motion
Scientific Method- on test know steps
systematic approach scientists use to learn about the laws of nature Steps: 1. Observe 2. Infur and hypothesize 3. Test/Expiriment 4. Conclude
Coordinate system- on test
the frame of reference we use in physics to describe motion
Define position-time graph- know
the position data is on the y- axis and the time data is on the x-axis it shows position relative to time shows position with respect to time
Definition of Phsyics- on test
the study of the fundamental laws of nature
The ________ of a ___________ is based soley on its _______ to account for known ________________ and correctly _________ new ones- know this
validity, hypothesis, ability, observations, predict The validity of a hypothesis is based soley on its ability to account for known observations and correctly predict new ones
Position Vector- on test
vector drawn from origin to object position -labeled with x -anytime object is in motion position is changing
What is the velocity equation what is the definition- on test
velocity = Displacement Δx/ time velocity- the rate at which you change direction and the rate of motion
A rose-covered parade float is at x = 0 at time t = 0. The float moves in a straight line at 2.0 m>s for the next 5 s before coming to a stop. After a 5-s stop, the float moves again at 1.0 m>s in the same direction as before. (a) Sketch the position-time graph for the float from the time t = 0 until the time t = 15 s. (b) From your graph, determine the positions of the float at t = 2 s and t = 11 s. This is on pg 56 #26- on test
when you graph remember that time is on the x-axis and position is on the y-axis xf= xi+vt xf = 0 +(2m/s)(2s) xf=4m Since we dont have a graph you must figure out how far the float went for the first 5 seconds then add that to after the float stoped for 5 seconds (or just quickly draw a graph) xf= 0 + (2m/s)(5s) xf= 10m remember that 10 seconds have passed from the time the float started to after it stoped for 5 seconds. It ran for 5 s then stoped for 5 seconds. Now you must find the position at t=11s xf 10m +(1m/s)(1s) xf= 10m +1m xf= 11m
The position-time equation of motion for a bunny hopping across a yard is xf = 8.3 m + (2.2 m>s)t (a) What is the initial position of the bunny? (b) What is the bunny's velocity? This is on pg 59 #35- on test
xf = 8.3 m + (2.2 m>s)t intial position is 8.3 m velocity is 2.2 m/s
You and a friend are at the airport, hurrying to the gate for your vacation flight to Hawaii. Your friend is well ahead and seems sure to get to the gate first. Just then you spot a moving walkway going your way. At the moment you step onto the walkway, your friend is 7.8 m ahead and walking with a speed of 2.30 m>s. Your speed on the walkway is 4.20 m>s. Show that you catch up with your friend at t = 4.10 s, and determine the location the two of you share at that time. -know
xf = xi + vt xf = 0 + (4.20m/s)(4.10s)= 17.2m xf = 7.8 + (2.30 m/s)(4.10s) = 17.2m You catch up with your friend in 4.10 s at the position x = 17.2 m, that is, 17.2 meters from the point where you stepped onto the moving walkway.
If you are at point 0 and you are moving at 2 m/s how far would you go in 3 s-know
xf = xi + vt xf = 0 + 2 m/s (3 s) xf = 6m
Displacement Equation- on test
Δx = xf - xi
