What is Average speed: Definition and 202 Discussions

In everyday use and in kinematics, the speed (commonly referred to as v) of an object is the magnitude of the rate of change of its position with time or the magnitude of the change of its position per unit of time; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance travelled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as the duration of the time interval approaches zero.
Speed has the dimensions of distance divided by time. The SI unit of speed is the metre per second (m/s), but the most common unit of speed in everyday usage is the kilometre per hour (km/h) or, in the US and the UK, miles per hour (mph). For air and marine travel the knot is commonly used.
The fastest possible speed at which energy or information can travel, according to special relativity, is the speed of light in a vacuum c = 299792458 metres per second (approximately 1079000000 km/h or 671000000 mph). Matter cannot quite reach the speed of light, as this would require an infinite amount of energy. In relativity physics, the concept of rapidity replaces the classical idea of speed.

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  1. mbisCool

    Simple average speed (quick glance should do the trick)

    Homework Statement A car travels up a hill at a constant speed of 30 km/h and returns down the hill at a constant speed of 66 km/h. Calculate the average speed for the round trip. Homework Equations avaerage speed= 2*speed1*speed2/(speed1+speed2) or average speed=total...
  2. S

    Traveling 10 Lightyears at 75% Speed - Time & Average Speed

    hi there looking for answers/explanation for this thought if a spaceship was to travel 10 light years at 75% the speed of light how long would it take(from the person inside the spaceships point off view) to travel 10 lightyears and what would be the average speed thanks
  3. J

    Average Speed Homework: Answer Check

    Homework Statement You walk for 1 min. at a speed of 1.5 m/s and then for 1 min at 4 m/s in a straight line. What is your average speed? The Attempt at a Solution (1.5 m/s + 4 m/s) / 2= 2.75 m/s Am I right? This is a very simple problem but I just want to double check myself.
  4. M

    What is the Average Speed of a Car Traveling Up and Down Hills?

    Homework Statement A car travels up a hill at 31 km/h and then down a hill at 59 km/h. Find the avg speed. Homework Equations The Attempt at a Solution I tried adding the speeds and then dividing by 2 but I guess that's definitely not how to approach this problem. How do I go...
  5. A

    Average velocity and average speed problem.

    Homework Statement The people move toward the door at a speed V s=3.50m/s,are each d=.25m in depth, and are separated by L=1.75 m. The arrangement in Fig.2=22 occurs at time t=0(a) at what average rate does the layer of people at the door increase? (b) at what time does the layer's depth...
  6. A

    Average velocity and average speed problem.

    Homework Statement Compute your average velocity in the following 2 cases: (a): You walk 73.2 m at a speed of 1.22 m/s and then run 73.2 m at a speed of 3.005 m/s along a straight line. Homework Equations this asks for average velocity which equals=change of x/change of t or...
  7. D

    What is the Average Speed Paradox?

    I take a certain journey and due to heavy traffic crawl along the first half of the complete distance of my journey at an average speed of 10 mph. How fast would I have to travel over the second half of the journey to bring my average speed to 20 mph? [This is Problem 10 on page 18 in...
  8. Z

    How Do You Calculate Average Speed for Different Return Speeds?

    Hello! Here is the question: A reconnaissance plane flies 520 km away from its base at 200 km/h, then flies back to its base at 400 km/h. What is its average speed? Okay so, 1040 is the total distance. I have to divide that by time...2hrs...I know the answer is roughly 267 km/h. But I...
  9. G

    Calculating Average Speed of Molecules

    [SOLVED] average speed Problem: Calculate the average speed of a molecule that strikes a small surface. How does this compare with the average speed of all molecules? I started by using the root mean square speed as the average speed of some random molecule, for example hydrogen. So...
  10. T

    How Is the Average Speed of Molecules Calculated?

    How do you caclulate the average speed of a molecule? Is it the same as the volume? Thank you for your time.
  11. Y

    Average speed with an unknown distance

    [SOLVED] Average speed with an unknown distance You travel from Place A to Place B, half the time at a speed of 60km/h and the other half at 100km/h. On the return journey, you travel half the distance at 60km/h, and the other half at 100km/h. a) What is your average speed from A to B? b)...
  12. A

    Average Speed? How do I calculate?

    Average Speed? How do I calculate?? How do I calculate average speed on a position time graph? Velocity time graph? Thanks Aaquib
  13. B

    Average Speed of Hydrogen molecules?

    What's the average speed of hydrogen molecules at room temperature and how do you figure it out? Is there an equation? thanks
  14. A

    How to Calculate Average Speed for a Commuter?

    [SOLVED] Average speed Hi, Please could someone enlighten me as to how to solve the following, given that the total time of the journey is not given? A commuter drives to work 14 miles. Due to traffic, the commuter averages 25 miles per hour on the first 7 miles of the drive. How fast must...
  15. R

    What Is the Average Speed of a Motorist Traveling Different Speeds?

    Homework Statement a motorist travels at 30 miles at 60 miles per hr, and then 60 miles at 30 miles per hr. what is the average speed Homework Equations The Attempt at a Solution I have tried to set this up and i get every answer, except 36 m/hr, can you please point me...
  16. R

    Understanding Average Speed Calculations

    Homework Statement theres a motorist that travels 30 miles at 60 mph, and another 60 miles at 30 mph. Homework Equations The Attempt at a Solution The average speed of the motorist is 36 mph how was this computed? i know avg speed is distance / chng of time however 30+...
  17. J

    Calculate the average speed from a bar graph

    Well I need to calculate the average speed from a bar graph and I do believe it said percent difference, then find the percent difference from the bar graph to my line graph. All I have is pictures of the bar graph, so can someone please tell me how to find the average speed and the percent...
  18. D

    Average speed & average velocity Problem

    Homework Statement Brandon is climbing a mountain. He starts from an elevation of H1=511m above sea level. In 6.18 hours he climbs to an elevation of H2=2746m above sea level. The length of his path is L1=16000m. A)What is the average angle of ascent the path makes with the...
  19. J

    Finding Average Speed and Velocity for a Round Trip

    First let me say hello as this is my first time here. I didn't do well in physics in high school, so most likely I will be on this site a lot for the next year or so. I've never used LaTeX before, but I will try my best to put equations in LaTeX format. I would also like to thank anyone that...
  20. Math Jeans

    Maxwell-Boltzmann Distribution and average speed

    Homework Statement Given the integral integral(0,infinity)(v^3*e^(-a*v^2)dv)=a^-2/2 Calculate the average speed v(average) of molecules in a gas using the Maxwell-Boltzmann distribution function. Homework Equations v^2(average)=integral(0,infinity)(v^2*v(t)dv) The Attempt at a...
  21. C

    Motion Problem, Find Average Speed

    Homework Statement Julie drives 100mi to Grandmother's house. On the way to Granmothers, Julie drives half the distance at 40mph and half the distance at 60mph. On the returntrip, she drives half the time at 40mph and half at 60mph. What is her average speed on the return trip...
  22. V

    Solving Bullet Speed and Time in Gun Barrel

    Homework Statement A bullet leaves the muzzle of a gun at a speed of 400 m/s. The length of the gun barrel is 0.50 m. Assuming the bullet was uniformly accelerated, (a) what was it's average speed inside the barrel? (b) how long was the bullet in the gun after it was fired? Homework...
  23. A

    What is the average speed during acceleration?

    Homework Statement A car is moving at a constant speed of 13 m/s when the driver presses down on the gas pedal and accelerates for 11 s with an acceleration of 1:4 m/s2. What is the average speed of the car during the period? Answer in units of m=s. The Attempt at a Solution using...
  24. L

    What is the average speed of a gerbil running in a clear plastic tube?

    Homework Statement What is its average speed during the first 35 s? (Figure shows the displacement-time graph of a gerbil running inside a straight length of clear plastic tubing.) Homework Equations any The Attempt at a Solution 2 m / 35 sec = .06 its wrong though
  25. M

    Average speed and deceleration

    hi. I'm fairly new at physics but i got put in AP Physics and i think i could make it with some help. Could anybody please explain how to solve this problem? A speed trap is set with 2 pressureactivated strips placed across a highway, 110 m apart. A car is speeding along at 33 m/s, while the...
  26. C

    Calculate the average speed in km/h of earth assuming a circular path

    I'm stuck on this math problem for my physics class, I'm sure it's not that difficult, but it confuses me: The Average distance between the Earth and the sun is 1.50 X 10^8 km. a. Calculate the average speed in km/h of Earth assuming a circular path about the sun. Use the equation v= 2TTr/T...
  27. R

    What Is the Average Speed of a Rabbit in a 4 km Race?

    Rabbits! Average Speed?? Homework Statement A rabbit takes part in a 4.00km race. First the rabbit runs 0.500 km then stops and takes a 90.0min nap. when he wakes up he runs twice as fast completing the race in a total time of 1.75h. A:-Calculate the average speed of the rabbit...
  28. T

    Determine the average speed for the car trip

    Homework Statement A person travels by car from one city to another with different constant speeds between pairs of cities. She drives for 15.0 min at 65.0 km/h, 20.0 min at 75.0 km/h and 60.0 min at 40.0 km/h, and spends 15.0 min eating lunch and buying gas. Determine the average speed for...
  29. T

    Calculating Average Speed of a Road Trip

    A person travels by car from one city to another with different constant speeds between pairs of cities. She drives for 15.0 min at 65.0 km/h, 20.0 min at 75.0 km/h and 60.0 min at 40.0 km/h, and spends 15.0 min eating lunch and buying gas. Determine the average speed for the trip. I know...
  30. B

    Average speed of earth in its orbit of sun

    Homework Statement The Earth's orbit around the sun is very nearly circular, with an average radius of 1.5x10^11 m. What is the average speed of the Earth in orbit around sun.Homework Equations d/t= 2pi/tThe Attempt at a Solution 2pi*1.5x10^11/ 31556926 it comes out to be 29865.95 answer is...
  31. F

    How Fast Must You Drive to Average 22 km/h Over 24 km?

    I have a question for anyone willing to help that I can't seem to figure out along with quite a few of my classmates: -You jog at 9.5 km/h for 8.0 km, then you jump into a car and drive an additional 16 km. With what average speed must you drive your car if your average speed for the entire...
  32. B

    What is the average speed of a cyclist on a round trip journey?

    1. The problem: A cyclist travels to work at an average speed of 3 m/s and returns home at an average of 9 m/s. Calculate the average speed for the whole journey. 2. Hints given by the teacher: The answer is not 6 m/s & the answer is around [approximately] 4.5 m/s. 3. The distance was...
  33. X

    Calculating Average Speed: Solving the Wedding Day Conundrum

    On your wedding day you leave for the church 36 minutes before the ceremony is to begin, which should be plenty of time since the church is only 9.0 miles away. On the way, however, you have to make an unanticipated stop for construction work on the road. As a result, your average speed for the...
  34. S

    Average speed between two points

    if i have to find the average speed between two points, do i just subtract distance2 from distance1 and divide by the time interval? so it could be possible for the average speed to be 0 if whatever traveled equally length in both negative and positive direction?
  35. C

    Average Speed vs. Average velocity

    Do you think that average speed and average velocities are usually the same for something in motion?
  36. H

    What is the Average Speed of a Plane?

    Suppose a plane flies 3470 miles from New York to London at an average speed of 1810 mi/h. Then the plane leaves London and flies to Los Angeles 5460 miles away with an average speed of 1437 mi/h. Find the average speed. I know that v(avg) = (delta)X/(delta) T. But my question is how do...
  37. V

    What is the average speed of the driver.

    A car travellinf at a uniform speed. The driver sees a milestone showing 2-digit number.After traveling for an hour the driver sees another milestone with same digits in reverse order. After another hour the driver sees another milestone containing the same 2 digits. What is the average speed of...
  38. S

    How Do You Calculate Average Speed During Acceleration?

    a car is moving at a constant speed of 11 m/s when the driver presses down the gas pedal and accelerates for 10 s with an acceleratiojn of 1.9 m/s. what is the average speed of the car during the period? I don't know which formula to use inorder to solve it. I tried using vbar= vo + v/2 and...
  39. J

    What is the average speed for this lap?

    ok, i am new at physics, so please no one make fun of me for my stupid questions. Ok here is the questions In the Canadian Grand Prix Auto race, the drivers travel a total distance of 304.3km in the 69 laps around the track. If the fastest lap time was 84.12s, what is the average speed for this...
  40. T

    Calculating Average Speed: Point 1 to Point 2 and Back, Using Identical Path

    You move from point 1 to point 2, and then from point 2 back to point1, using the identical path. if your average speed from point 1 to point 2 is S1 and the average speed from point 2 back to point 1 is S2. What's the average speed of the entire trip there and back, in terms of S1 and S2...
  41. O

    Average speed and average velocity?

    Average speed and average velocity?? Hello Dose a particle having a uniform circular motion may have some average velocity, although it is accelerating?? And how to find it? If yes, it has some average velocity then, what's its relation with average speed? "IAM CONFUSED THAT...
  42. A

    Average Speed: 30km/hr Explained

    If the average speed going to town is 40km/hr, and return at an average speed of 60 km/hr. what is the average speed? why is it not 50 km/hr Is the answer 30? because he goes 40 km/hr for 1 1/2 hours. etc.
  43. C

    Finding Total Vector Displacement for a Multi-Directional Trip

    The problem is: A motorist drives south at 20.0 m/s for 3.00 min, then turns west and travels at 25.0 m/s for 2.00 min, and finally travels northwest at 30.0 m/s for 1.00 min. For this 6.00-min trip, find (a) the total vector displacement, (b) the average speed, and (c) the average velocity...
  44. O

    Race car minimum average speed

    Not asking for an answer, just point me in the right direction please: In order to qualify for a racing event, a race car must achieve an average speed of 278km/h on a track with a total length of 1260m. If a particular car covers the first half of the track at an average speed of 209km/h...
  45. P

    Calculating Average Speed: A Problem-Solving Dilemma

    I've got a little trouble here with average speed. The specific problem is: A paper delivery boy rides his bike 2 miles out to a farmhouse at 12mph, delivers the paper, then travels back 2 miles at 10mph to get home. What was the delivery boy's average speed during this trip? (Hint: there...
  46. S

    Calculating Average Speed of a Tapir

    A wandering tapir trots along at 9 ft/s for 9 minutes, then walks at 6 ft/s for 7 minutes, and finally runs at 27 ft/s for 1 minutes. How do I find the average speed of the tapir ? I have already added the numerators and denominators then divided by 3
  47. P

    Average speed that you observe for the button as it falls

    You are at an airport watching people go by on a "people mover" conveyer belt that moves at a constant speed of 0.60m/s. As a person goes by, they drop a button from a height of 1.2m. What is the average speed that you observe for the button as it falls to the ground? well i have: x=1.2m...
  48. M

    Solve Average Speed Problem: How to Qualify for a Race with Engine Trouble?

    Hi I am having problem with this question and keep getting the wrong answer. 1. A racecar driver must average 200km/h for four laps to qualify for a race. Because of engine trouble, the car averages only 170km/h over the first two laps. What average speed must be maintained for the last two...
  49. O

    What Is Julie's Average Speed to and from Grandmother's House?

    Julie drives 100 mi to Grandmother's house. On the way to Grandmother's, Julie drives half the distance at 50.0 and half the distance at 76.0. On her return trip, she drives half the time at 50.0 and half the time at 76.0. they are looking for average speed to grannys house and then from...
  50. H

    What is your average speed from Houston back to San Antonio?

    Plz show me how to do #1? and please check my work on #2 and 3. thanks so much! :smile: 1) You drive on Interstate 10 from San Antonio to Houston, half the time at 55km/h and the other half at 90km/h. On the way back you travel half the distance at 55km/h and the other half at 90km/h...
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