Average speed Definition and 202 Threads

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. Y

    What is its average speed during this 37 s interval? Answer in units o

    What is the magnitude of the instantaneous velocity (speed) of a freely falling object 37 s after it is released from a position of rest? Consider the acceleration of gravity to be 10 m/s2 . Answer in units of m/s What is its average speed during this 37 s interval? Answer in units of m/s
  2. C

    Average Speed between two cities

    Pauline travels between two cities. First she drives for 31 minutes at an average speed of 82 km/hr then for 23 minutes at an average speed of 51 km/hr, then she spends 25 minutes eating lunch and buying gas, and then she drives for 15 minutes at an average speed of 44 km/hr. Find Pauline’s...
  3. P

    Displacement, Average Speed, and Average Velocity

    Okay so I don't understand how to do the displacement of distance and time on a graph. I also need help with figuring out the average speed and average velocity. The graph deals with a Turtle's journey. On the Y-axis of the graph is distance in meters and the x-axis is time in minutes. The...
  4. C

    His average speed for the first 4km is what?

    A man runs a distance of 9km at a constant speed for the first 4km and then 2km/h faster for the rest of the distance. The whole run takes him one hour. His average speed for the first 4km is what? Total distance = 9km Total time = 1 h For the 1st for 4km, he moved at a constant...
  5. Y

    I am having a problem with this question - average speed of a car

    Homework Statement a car travels along a straight path at a constant speed of 60mi/h for a distance d and then another distance d in the same direction at another constant speed the average velocity over the entire trip is 30mi/h what is the constant speed with which the car moved during...
  6. E

    Just a few questions - calculating the average speed and John's speed

    Normally I would ask my teacher, but since we had the day off and it's due the day we get back, I can't question him. Homework Statement What is the difference between calculating the average speed and John's speed (questions g and f)? and how do you find displacement for a distance-time...
  7. N

    Average Speed vs. Instantaneous Speed

    Homework Statement A book falls off a shelf and lands on the floor. Which is greater, the book's average speed or its instantaneous speed right before it lands? Homework Equations v = d/t The Attempt at a Solution I think its the instantaneous speed because the book accelerates...
  8. R

    What Is the Difference Between Average Speed and Velocity in Tyler's Journey?

    Very simple question -- Average speed for a journey Homework Statement Tyler travels a distance (in a straight line) of 18km in 30minutes. iii)Tyler Returns home following the same route in the same amount of time. Write down her average speed and velocity for this journey, explaining why...
  9. C

    MHB Find the average speed of the ball

    the height in ft of a baseball, t seconds after being thrown straight upward, is given by h(t)=36t - 16t^2 1) find the average speed of the ball for a) 0≤ t ≤1 b) .5≤ t ≤ 1 c) .9 ≤ t ≤1 the answer to a) is 20 ft/sec, which is what you get if you plug 1 into the equation. the answer to b)...
  10. D

    Distance Traveled & Average Speed

    Homework Statement A driver maintains a steady speed of 30.0 m/s for 55 min and then slows to 10 m/s for the next 5 mins. Determine the the total distance traveled and the average speed for the trip. Homework Equations a = v−v0/t The Attempt at a Solution a = 30 - 10 / 60...
  11. X

    Average speed of person walking problem

    Homework Statement A person walks first at a constant speed 5m/s along a straight line from point A to point B, and then back along the line from B to A at a constant speed 3m/s. (a) What is her average speed over the entire trip? (b) Her average velocity over the entire trip? Homework...
  12. E

    Ambiguity in forumlas for average speed & average velocity

    I'm going to start with an example: On her way to school, a child discovered that her loonie is missing and there is a hole in her pocket. She turned back and walked 24 m east along the sidewalk. Then, she stopped for 18 s and decided to head back to school. After walking 11 m west, she found...
  13. B

    Average speed of person walking

    A person walks first at a constant speed of 5.00 m/s along a straight line from point A to point B and then back along the line from B to A at a constant speed of 3.00 m/s. What are (a) her average speed over the entire trip and (b) her average velocity over the entire trip? I already solved...
  14. C

    Clarification between average velocity and average speed

    To find average velocity, you do total displacement over total time To find average speed, you add up the speeds / total speeds there are? (Eg. (10+20)/2) Am I correct?
  15. V

    Find the average speed from t = 0 to t = 1 s

    Homework Statement The position of a particle as a function of time is given by x = (6 m/s)t + (-2 m/s^2)t^2. Find the average speed from t = 0 to t = 1 s ---------------------------------------------------------------------------------------Also, how would I plot x versus t for t = 0 to t =...
  16. S

    Which body has the higher average speed?

    Homework Statement Two bodies travel the same distance. One body travels half of the distance with the speed V and the other half with the speed 2V. The second body travels half of the time with the speed V and the other half of the time with the speed 2V. Which of the bodies has the higher...
  17. O

    What Is the Ball's Average Speed During the First 2.7 Seconds?

    Hey guys so I'm stuck and only have a couple tries left meaning I've lost quite some marks on this question already and I can't risk anymore so the question is... A ball moves in a straight line (the x-axis). The graph in the figure (Figure 1) shows this ball's velocity as a function of time...
  18. T

    Apparent forces problem, train of average speed and a difference in weight

    Homework Statement While taking an eastbound train to work, a passenger of fixed mass finds that she weighs 542N. On the way home she weighs herself again while the train is at full speed and finds she weighs 543N. If she works 50km from home, how long is her commute if she lives at 40°S...
  19. N

    What is the average speed for the entire trip?

    Homework Statement A commuting student leaves home and drives to school at an average speed of 40.0 km/h. After 24.0 min he realizes that he has forgotten his homework and returns home to get it at the same average speed. It takes 9.0 min to find the report, after which the trip to school 40.0...
  20. C

    How Do You Calculate Average Speed in a Mixed-Speed Relay?

    Homework Statement The cheetah can run as fast as 113 km/h, the falcon can fly as fast as 161 km/h, and the sailfish can swim as fast as 105 km/h. The three of them run a relay with each covering a distance L at maximum speed. What is the average speed of this relay team for the entire...
  21. G

    Why Does Average Speed Calculation Differ for Uphill and Downhill Travel?

    Homework Statement A Bus drives 1km up a hill in 5.0 minutes. It then drives down the hill in 4.0 minutes. For the bus, find a) the average speed up the hill b) the average speed down the hill c)the average speed for the whole trip d)why is the answer for c) not equal to (speed up the hill +...
  22. P

    Race Car Driver's Average speed

    A race car driver must average 200.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h , what average speed must be maintained for the last lap? Avg Speed=Distance traveled/Time 218 km/h, I averaged the first 9 laps at 198 and plugged the...
  23. P

    What type of molecule has the highest average speed in a room filled with gases?

    Homework Statement The gases in this room include oxygen (molar mass 32 g), nitrogen (28 g), water (18 g), and carbon dioxide (44 g). Which type of molecule has the highest average speed? A) O2 B) N2 C) H2O D) CO2 E) They have the same average speed. Homework Equations...
  24. R

    Average Speed Of a and b where d and t is not given

    A body covers half its journey with a speed of a m/s and the other half with a speed of b m/s Calculate the average speed of the body during the whole journey
  25. B

    What is the Average Speed Computation Problem on a Hill?

    Homework Statement The problem is in the provided link (it is questions 2.2) http://www.docstoc.com/docs/3817109/Chapter-Problems-A-car-travels-up-a-hill-at-a Homework Equations The Attempt at a Solution I understand the duration of time it takes to go up the hill is a larger time...
  26. C

    How Do You Calculate Average Speed from Displacement-Time Data?

    Homework Statement Use the data table of displacement time data to get a line of best fit using your Ti-83 calculator. Once you have the equation, graph it so that you can answer the questions 1-5 that follow. Assume that the data below is for an object that is launched vertically upwards...
  27. J

    Finding average speed on a velocity vs time graph

    Hello, Again I find my self struggling on a question I had on a test, as my teacher is a "general studies" teacher, she is not much help with physics. the question is: What is the average speed of the car for the 10 second interval? I have uploaded the graph provided, if you can't...
  28. N

    Period of arbitrary amplitude pendulum using average speed

    Homework Statement A simple pendulum of length L is pulled aside to angle θm then released from rest. For arbitrary angle θ on the path of motion the acceleration along the path is -gSinθ. The speed at this point is V(θ)= √[2gL (cos θ - cos θm)]. Find the period T of the pendulum (do not...
  29. G

    Solving for Car's Acceleration, Time, and Average Speed

    Homework Statement A car is initial at rest. It accelerates over a distance of 1250m and reaches a speed of 112 km/h. Find: A) the acceleration for the car B) the time it took for it to reach this final speed C) the average speed Homework Equations A = delta V/ delta T or v^2 = V...
  30. O

    Average Velocity and Average Speed of Integral

    Homework Statement An object moves with velocity v(t) = −t2 +1 feet per second between t = 0 and t = 2. Find the average velocity and the average speed of the object between t = 0 and t = 2 Homework Equations \frac{1}{b-a} \int_a^b f'(x) dx avg value of a function The Attempt...
  31. W

    Can anyone help with an average speed problem?

    Homework Statement A racing team of 3 drivers drove a 24 hour event in shifts. The first driver drove only one fourth of the race but averaged 140km/hr. The second driver drove one third of the race at an average speed of 170 km/hr. The last driver drove the remainder of the race at 160...
  32. R

    Difference between Average Speed & Average Velocity in Velocity-Time graphs?

    I just want to know what is the difference on how to find Average velocity and Average speed when I try to find it in Velocity-Time graphs Also how do you find distance traveled and displacement in these velocity-time graphs. Thanks in advance for your help. Please use fairly simple...
  33. L

    Calculating Average Speed: Step-by-Step Guide for East and North Travel

    Homework Statement A car travels east at 86 km/h for 6 h. It then travels 50.0° east of north at 112 km/h for 6 h. (a) What is the average speed for the trip? How do I solve for the average speed?
  34. I

    How do I find the average speed for this problem?

    Homework Statement I don't know how to start.. someone please give me a step-by-step explanation. Julie drives 100 mi to Grandmother's house. On the way there she drives half of the distance at 42 mi/hr and half the distance at 68 mi/hr. What is Julie's average speed (in mi/hr) on the way to...
  35. J

    Average velocity just simply be the average speed

    Hi peeps, i just started intro physics but finding it sort of difficult, and attempting to do some questions but just not quite sure if I am doing it right. would so appreciate any kind of help, my teacher doesn't seem to break it down enough for me lol. can somebody just check my work, and let...
  36. A

    Calculating Average Speed and Velocity for a Commuting Student

    Homework Statement A commuting student leaves home and drives to school at an average speed of 42.0 km/h. After 22.0 min she realizes that she has forgotten her homework and returns home to get it at the same average speed. It takes 8.0 min to find the report, after which the trip to school...
  37. S

    Average Speed Vs. Direct Average?

    I'm having trouble differentiating between the definition of average in physics and a traditional average. For example, say a car travels 100km for 2 hours then travels 80km for 1 hour. The average speed for the first portion is 50km/hr and the average speed for the second portion is 80km/hr...
  38. P

    Zero average speed but nonzero average velocity?

    Homework Statement Is it possible to have zero average speed but nonzero average velocity? Homework Equations The Attempt at a Solution This is probably completely wrong, but I'll put it up anyway: If one's frame of reference is also the center of an arbitrary circle, then an...
  39. F

    Initial speed of a football when average speed is known

    Hi First of all, this is not a homework question, but I'm sorry if it's in the wrong sub-forum. I know that a football (soccer) has been kicked a distance of 5 meters using 0,16 seconds, that would give an average speed of 112,5 km/h, or approx 31 m/s. But since the speed of a football is...
  40. C

    How Do You Calculate Average Speed for a Two-Part Journey?

    Homework Statement A car is driven 19 km at an average speed of 91 km/h and after that 61 km at an average speed of 65 km/h. Homework Equations What was the average speed of the whoIe joumey? The Attempt at a Solution t1=19/91 = 0.208 h t2=61/65 = 0.938 h average speed =...
  41. alyafey22

    Instantaneous and average speed

    Can instantaneous and average speed be equal to each other in any why ? if it can can you please give me an example ??
  42. R

    How Is Average Speed Calculated for a Round Trip with Different Speeds?

    Homework Statement If you drive from Physicsland to Chemistryland at a constant speed of 120 km/h and immediately return at a constant speed of 60.0 km/h, what is your average speed? Homework Equations The Attempt at a Solution Somebody helped me out on this question and we used a...
  43. S

    Why Can We Only Calculate Average Speed During a Stone's Fall?

    1. Explain why we can only calculate a stone's average speed during its fall. Hope someone can help, thanks
  44. V

    What Average Acceleration Must a Plane Achieve for Safe Takeoff?

    Homework Statement An airport has runways only 174 m long. A small plane must reach a ground speed of 42 m/s before it can become airborne. What average acceleration must the plane’s engines provide if it is to take off safely from its airport? Answer in units of m/s 2 . Homework...
  45. F

    Average Speed Between Points A & B: 0 m/s

    A person walks first at a constant speed of 5.01 m/x along a straight line from point A to B and then back along the line from B to A at a constant speed of 3.10 m/s What is the average speed over the entire trip? I've tried everything from adding the two and dividing by two. I've found...
  46. C

    What is the average speed of a particle with given position and time data?

    Homework Statement The position of a particle as a function of time is given by x = (-5.06 m/s)t + (3.05 m/s2)t2. Calculate the average velocity of the particle from t = 0 to t = 1.20 s. -1.40 m/s (this is correct, from my calculations) 2nd part: Calculate the average speed from t = 0 to...
  47. P

    Short homework check (average speed)

    Homework Statement Hey guys, I just want you to check out my homework before I send it off! First of all, I attached a table in which I was required to come up with “Time per mode of transport” and “Total time to reach final destination” I included my answers right on the table in the...
  48. P

    Significant digits and easy average speed/ velocity questions

    Homework Statement Here is a few examples where i am wondering as to how many significant digits to leave 3.5L/100km * 2279km = 79.765 ---> In this case am i supposed to round to 2 significant digits because of 3.5 which has two? 1.2L/100km * 63km = 0.756, i leave it as 0.76 right...
  49. T

    Velocity time graph with distance and average speed

    I know how to work out velocity once you have the graph, I'm just not sure if i can do the graph with distance and average speed. So, can you work out velocity from a graph with distance and average speed?
  50. murshid_islam

    A question about average speed

    If we travel s1 distance in t1 time and s2 distance in t2 time, is the average speed \frac{s_1 + s_2}{t_1 + t_2} or \frac{\frac{s_1}{t_1} + \frac{s_2}{t_2}}{2}
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